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• 351. [Article] Relationships of green-tree retention following timber harvest to forest growth and species composition in the western Cascade Mountains

  National Forest management in the Pacific Northwest is shifting from a focus on commodity production to ecosystem management, in which the health of the entire forest ecosystem is considered, rather than ...

  Citation × Citation Citation Abstract Copy Title: Relationships of green-tree retention following timber harvest to forest growth and species composition in the western Cascade Mountains Author: Rose, Coulter R. National Forest management in the Pacific Northwest is shifting from a focus on commodity production to ecosystem management, in which the health of the entire forest ecosystem is considered, rather than that of a few key species. Ecosystem management includes retention of some live trees following timber harvest (green-tree retention) to preserve biodiversity, imitating the natural fire regime of large, but patchy fires that leave many live trees. How ecosystem management will affect growth and species composition of future forests is an important question. This study takes a retrospective approach to this question by using past disturbance as an analogue to green-tree retention following timber harvest. Using USDA Forest Service timber inventory plot data from the Cascade Mountains of Oregon and SW Washington, 132 unmanaged stands were identified with a tree cohort of 70-110 years old (regeneration) or a tree cohort of 70-110 years old with an overstory of large trees 200+ years old (remnants). All stands were in the Tsuga heterophylla (Raf.) Sarg. zone (Franklin and Dyrness 1973). Single-aged stands represented clearcuts, while two-aged stands served as analogues to stands harvested with green-tree retention. Regeneration basal area/hectare (ba/ha) declined when remnant-tree densities exceeded about 15 remnant trees/ha (R²=0.51) in a relationship roughly described by a sigmoidal curve. Conceptually removing remnant-tree space occupancy effects decreased remnant-tree density's value as a predictor of regeneration ba/ha by about 50% at management-level remnant densities (≤45 remnant trees/ha). Thus, it appears that remnant "effects" were a result of both remnant-tree space occupancy and remnant resource use. Douglas-fir ba/ha in the regeneration also declined when remnant-tree densities exceeded about 15 remnant trees/ha (R²=0.60). Western hemlock ba/ha in the regeneration increased slightly with increasing remnant-tree densities (R²=0.19). Western redcedar ba/ha in the regeneration was apparently not related to remnant-tree density (R²=0.02). The degree of aggregation in remnant trees did not appear to affect regeneration ba/ha, but few stands contained the isolated clumps of remnant trees likely under a management scenario. Neither measured site characteristics nor regeneration density was related to regeneration ba/ha across species. Remnant-tree density was apparently unrelated to tree-species diversity in the regeneration. Total-stand ba/ha remained relatively constant across remnant densities. Title: Relationships of green-tree retention following timber harvest to forest growth and species composition in the western Cascade Mountains Author: Rose, Coulter R. National Forest management in the Pacific Northwest is shifting from a focus on commodity production to ecosystem management, in which the health of the entire forest ecosystem is considered, rather than that of a few key species. Ecosystem management includes retention of some live trees following timber harvest (green-tree retention) to preserve biodiversity, imitating the natural fire regime of large, but patchy fires that leave many live trees. How ecosystem management will affect growth and species composition of future forests is an important question. This study takes a retrospective approach to this question by using past disturbance as an analogue to green-tree retention following timber harvest. Using USDA Forest Service timber inventory plot data from the Cascade Mountains of Oregon and SW Washington, 132 unmanaged stands were identified with a tree cohort of 70-110 years old (regeneration) or a tree cohort of 70-110 years old with an overstory of large trees 200+ years old (remnants). All stands were in the Tsuga heterophylla (Raf.) Sarg. zone (Franklin and Dyrness 1973). Single-aged stands represented clearcuts, while two-aged stands served as analogues to stands harvested with green-tree retention. Regeneration basal area/hectare (ba/ha) declined when remnant-tree densities exceeded about 15 remnant trees/ha (R²=0.51) in a relationship roughly described by a sigmoidal curve. Conceptually removing remnant-tree space occupancy effects decreased remnant-tree density's value as a predictor of regeneration ba/ha by about 50% at management-level remnant densities (≤45 remnant trees/ha). Thus, it appears that remnant "effects" were a result of both remnant-tree space occupancy and remnant resource use. Douglas-fir ba/ha in the regeneration also declined when remnant-tree densities exceeded about 15 remnant trees/ha (R²=0.60). Western hemlock ba/ha in the regeneration increased slightly with increasing remnant-tree densities (R²=0.19). Western redcedar ba/ha in the regeneration was apparently not related to remnant-tree density (R²=0.02). The degree of aggregation in remnant trees did not appear to affect regeneration ba/ha, but few stands contained the isolated clumps of remnant trees likely under a management scenario. Neither measured site characteristics nor regeneration density was related to regeneration ba/ha across species. Remnant-tree density was apparently unrelated to tree-species diversity in the regeneration. Total-stand ba/ha remained relatively constant across remnant densities. Close

• 352. [Article] Effects of pesticides on amphibians with special reference to the pyrethroid insecticide, cypermethrin

  Pollution by pesticides is a ubiquitous concern for wildlife. The effects of pesticides are especially concerning in aquatic environments, which are particularly vulnerable as they have several exposure ...

  Citation × Citation Citation Abstract Copy Title: Effects of pesticides on amphibians with special reference to the pyrethroid insecticide, cypermethrin Author: Biga, Lindsay M. Pollution by pesticides is a ubiquitous concern for wildlife. The effects of pesticides are especially concerning in aquatic environments, which are particularly vulnerable as they have several exposure routes for the influx of chemicals. These effects are of particular concern as biodiversity loss reaches unprecedented rates. This includes recent declines of amphibian populations and loss of amphibian species. Pesticide exposure may contribute to some amphibian populations and extinctions. This dissertation explores the effects of pesticides on amphibians, with particular reference to the pyrethroid insecticide cypermethrin. I first synthesized acute toxicity data of pesticides for amphibians from the literature (Chapter 2). Using 96h LC50 values for amphibian larvae exposed to insecticides, herbicides, and fungicides, I determined that amphibian species cannot be systematically classified as sensitive or tolerant to pesticides. Rather, relative acute lethal toxicities varied among species and between chemicals and types of pesticides even within a species, indicating that no amphibian species from this analysis can represent anticipated toxic effects to all amphibians. I next examined the differences in sensitivity to cypermethrin among three developmental stages for three anuran (frog) species (Chapter 3). I experimentally exposed embryos, recently hatched larvae and larvae with limb buds to cypermethrin in the laboratory. Exposure to cypermethrin had lethal and sublethal effects on some species and stages, but not all. The Pacific treefrog (Pseudacris regilla) was the most sensitive species and the early larval stage was the most sensitive for these three species. Additionally, cypermethrin exposure induced abnormal behavior in response to prodding for some species and stages. These results indicate differences in sensitivity to cypermethrin among species of amphibians. To further understand differences in sensitivity to pesticides among amphibians, I compared how three populations of P. regilla responded to cypermethrin exposure (Chapter 4). I performed a time-to-death assay in the laboratory, exposing newly hatched larvae from each population to cypermethrin under identical conditions. All populations had high rates of mortality when exposed to cypermethrin compared to unexposed controls and populations varied in the time to death. Moreover, exposed individuals were smaller than unexposed controls. Interestingly, population sensitivity did not appear to be associated with proximity to agriculture, but rather with elevation gradient, indicating that an evolved tolerance to pesticide exposure is not the mechanism for the differences in sensitivity observed here. To investigate the effects of cypermethrin on amphibians within a community context, I studied exposure in mesocosms (Chapter 5). I set up semi-natural aquatic ponds in enclosures that contained zooplankton, phytoplankton, and periphyton along with amphibian larvae. I experimentally exposed these mesocosms to cypermethrin and measured the effects on the amphibians and the other members of the community. Cypermethrin affected the entire aquatic community, even at the lowest dose, indicating the direct and indirect deleterious effects of cypermethrin on both invertebrate and vertebrate species in an aquatic community. This dissertation provides needed data on the effects of the pyrethroid insecticide cypermethrin on amphibians and their communities. Understanding the toxicity of newer, commonly used pesticides to non-target organisms is important as conservation biologists and managers make efforts to combat future amphibian population declines which may be associated with chemicals in the environment. Title: Effects of pesticides on amphibians with special reference to the pyrethroid insecticide, cypermethrin Author: Biga, Lindsay M. Pollution by pesticides is a ubiquitous concern for wildlife. The effects of pesticides are especially concerning in aquatic environments, which are particularly vulnerable as they have several exposure routes for the influx of chemicals. These effects are of particular concern as biodiversity loss reaches unprecedented rates. This includes recent declines of amphibian populations and loss of amphibian species. Pesticide exposure may contribute to some amphibian populations and extinctions. This dissertation explores the effects of pesticides on amphibians, with particular reference to the pyrethroid insecticide cypermethrin. I first synthesized acute toxicity data of pesticides for amphibians from the literature (Chapter 2). Using 96h LC50 values for amphibian larvae exposed to insecticides, herbicides, and fungicides, I determined that amphibian species cannot be systematically classified as sensitive or tolerant to pesticides. Rather, relative acute lethal toxicities varied among species and between chemicals and types of pesticides even within a species, indicating that no amphibian species from this analysis can represent anticipated toxic effects to all amphibians. I next examined the differences in sensitivity to cypermethrin among three developmental stages for three anuran (frog) species (Chapter 3). I experimentally exposed embryos, recently hatched larvae and larvae with limb buds to cypermethrin in the laboratory. Exposure to cypermethrin had lethal and sublethal effects on some species and stages, but not all. The Pacific treefrog (Pseudacris regilla) was the most sensitive species and the early larval stage was the most sensitive for these three species. Additionally, cypermethrin exposure induced abnormal behavior in response to prodding for some species and stages. These results indicate differences in sensitivity to cypermethrin among species of amphibians. To further understand differences in sensitivity to pesticides among amphibians, I compared how three populations of P. regilla responded to cypermethrin exposure (Chapter 4). I performed a time-to-death assay in the laboratory, exposing newly hatched larvae from each population to cypermethrin under identical conditions. All populations had high rates of mortality when exposed to cypermethrin compared to unexposed controls and populations varied in the time to death. Moreover, exposed individuals were smaller than unexposed controls. Interestingly, population sensitivity did not appear to be associated with proximity to agriculture, but rather with elevation gradient, indicating that an evolved tolerance to pesticide exposure is not the mechanism for the differences in sensitivity observed here. To investigate the effects of cypermethrin on amphibians within a community context, I studied exposure in mesocosms (Chapter 5). I set up semi-natural aquatic ponds in enclosures that contained zooplankton, phytoplankton, and periphyton along with amphibian larvae. I experimentally exposed these mesocosms to cypermethrin and measured the effects on the amphibians and the other members of the community. Cypermethrin affected the entire aquatic community, even at the lowest dose, indicating the direct and indirect deleterious effects of cypermethrin on both invertebrate and vertebrate species in an aquatic community. This dissertation provides needed data on the effects of the pyrethroid insecticide cypermethrin on amphibians and their communities. Understanding the toxicity of newer, commonly used pesticides to non-target organisms is important as conservation biologists and managers make efforts to combat future amphibian population declines which may be associated with chemicals in the environment. Close

• 353. [Article] Evolutionary Insights into Cnidarian-Dinoflagellate Symbiosis from Natural Variation in Aiptasia Sea Anemones

  Mutualistic associations between corals and symbiotic microalgae of the genus Symbiodium power tropical reef ecosystems, hotspots of marine biodiversity that buffer coastlines, support tourism- and fisheries-based ...

  Citation × Citation Citation Abstract Copy Title: Evolutionary Insights into Cnidarian-Dinoflagellate Symbiosis from Natural Variation in Aiptasia Sea Anemones Author: Bellis, Emily S Mutualistic associations between corals and symbiotic microalgae of the genus Symbiodium power tropical reef ecosystems, hotspots of marine biodiversity that buffer coastlines, support tourism- and fisheries-based economies, and offer untapped potential for discovery of novel pharmaceutical compounds. However, reef ecosystems are declining at an alarming rate, in large part due to severe episodes of coral bleaching, or breakdown of the coral-Symbiodinium symbiosis. The sea anemone Aiptasia has emerged as a laboratory model system for understanding coral-Symbiodinium interactions at multiple biological levels. To further develop Aiptasia as an evolutionary model system, the goal of my dissertation work was to characterize natural variation in Aiptasia-Symbiodinium symbioses by (1) examining genome-wide polymorphism among global anemone lineages, (2) experimentally evaluating natural variation in bleaching response, and (3) investigating patterns of genetic variation in natural populations across diverse abiotic environments. In Chapter 2, I use low-coverage genome skimming to investigate polymorphism in well-studied laboratory strains hosting diverse Symbiodinium, revealing that higher genetic diversity exists in Aiptasia from the Western Atlantic compared to a more globally distributed lineage. I further compare polymorphisms in sliding windows across the genome to identify candidate genes under balancing and positive selection based on patterns of heterozygosity, nucleotide diversity, and Tajima’s D. In Chapter 3, I characterize bleaching of Aiptasia lab strains to different stressors and discover significant variation in responses to acute heat stress but not to cold-shock. In Chapter 4, I examine potential relationships between abiotic environmental variation and genetic variation of anemone-Symbiodinium assemblages in the wild, at four locations in Caribbean Panama where long-term environmental datasets are available. High-throughput genotyping of anemone populations revealed the presence of a closely related cryptic species, Exaiptasia brasiliensis, and striking differences in anemone abundance, distribution, and patterns of symbiont association across environments. An Aiptasia sub-population specific to the Bocas del Toro Archipelago is described, with strong differentiation compared to the global population at several loci predicted to be important for mediating interactions with Symbiodinium. Analyses further suggest that the spatial extent of clonal reproduction in natural populations could be somewhat limited. Overall, Chapters 2-4 support a widespread global Aiptasia population distributed throughout tropical and subtropical latitudes with one or more diverged lineages, diversity of both host lineages and holobiont assemblages centered in the tropical Western Atlantic, and holobiont distribution patterns that may be strongly influenced by abiotic environment. Future studies leveraging natural variation in the Aiptasia model system described here hold great promise for advancing our fundamental knowledge of the evolution of symbiotic interactions in the sea. Title: Evolutionary Insights into Cnidarian-Dinoflagellate Symbiosis from Natural Variation in Aiptasia Sea Anemones Author: Bellis, Emily S Mutualistic associations between corals and symbiotic microalgae of the genus Symbiodium power tropical reef ecosystems, hotspots of marine biodiversity that buffer coastlines, support tourism- and fisheries-based economies, and offer untapped potential for discovery of novel pharmaceutical compounds. However, reef ecosystems are declining at an alarming rate, in large part due to severe episodes of coral bleaching, or breakdown of the coral-Symbiodinium symbiosis. The sea anemone Aiptasia has emerged as a laboratory model system for understanding coral-Symbiodinium interactions at multiple biological levels. To further develop Aiptasia as an evolutionary model system, the goal of my dissertation work was to characterize natural variation in Aiptasia-Symbiodinium symbioses by (1) examining genome-wide polymorphism among global anemone lineages, (2) experimentally evaluating natural variation in bleaching response, and (3) investigating patterns of genetic variation in natural populations across diverse abiotic environments. In Chapter 2, I use low-coverage genome skimming to investigate polymorphism in well-studied laboratory strains hosting diverse Symbiodinium, revealing that higher genetic diversity exists in Aiptasia from the Western Atlantic compared to a more globally distributed lineage. I further compare polymorphisms in sliding windows across the genome to identify candidate genes under balancing and positive selection based on patterns of heterozygosity, nucleotide diversity, and Tajima’s D. In Chapter 3, I characterize bleaching of Aiptasia lab strains to different stressors and discover significant variation in responses to acute heat stress but not to cold-shock. In Chapter 4, I examine potential relationships between abiotic environmental variation and genetic variation of anemone-Symbiodinium assemblages in the wild, at four locations in Caribbean Panama where long-term environmental datasets are available. High-throughput genotyping of anemone populations revealed the presence of a closely related cryptic species, Exaiptasia brasiliensis, and striking differences in anemone abundance, distribution, and patterns of symbiont association across environments. An Aiptasia sub-population specific to the Bocas del Toro Archipelago is described, with strong differentiation compared to the global population at several loci predicted to be important for mediating interactions with Symbiodinium. Analyses further suggest that the spatial extent of clonal reproduction in natural populations could be somewhat limited. Overall, Chapters 2-4 support a widespread global Aiptasia population distributed throughout tropical and subtropical latitudes with one or more diverged lineages, diversity of both host lineages and holobiont assemblages centered in the tropical Western Atlantic, and holobiont distribution patterns that may be strongly influenced by abiotic environment. Future studies leveraging natural variation in the Aiptasia model system described here hold great promise for advancing our fundamental knowledge of the evolution of symbiotic interactions in the sea. Close

• 354. [Article] Political economy and trade effects of invasive species regulation : the case of noxious weeds

  Many non-native weed pests of food, fiber, and nursery crops pose threats to U.S. environment and agriculture. Noxious weed regulations play an important role in preventing the introduction and spread ...

  Citation × Citation Citation Abstract Copy Title: Political economy and trade effects of invasive species regulation : the case of noxious weeds Author: Min, He Many non-native weed pests of food, fiber, and nursery crops pose threats to U.S. environment and agriculture. Noxious weed regulations play an important role in preventing the introduction and spread of non-native plants, thereby protecting the local biodiversity, environment and economic activities. However, these regulations could also hamper agricultural trade. The three essays of this dissertation address the causes and consequences of cross-state differences in noxious weed regulations. In the first essay, a political-economic model is developed to derive cross-state regulatory congruence as a function of ecological and agronomic characteristics, and interest-group lobbying through political contributions. Econometric estimation suggests ecological and agronomic dissimilarities are primary causes of cross-state differences in noxious weed regulation. However, evidence of lobbying effects is statistically and economically significant. In particular, agricultural seed producers favor more uniform weed regulations across states, while commodity producers and consumers prefer that their state maintain a distinct weed list to protect its ecosystem and agronomic conditions. The impact of noxious weed regulations on inter-state agricultural trade is measured in the second essay. In particular, the extent of trade distortions arising from interest-groups' lobbying is estimated. For this purpose, each state’s net trade in three industries - agricultural seeds, nursery products and commodities - is derived as a function of weed regulatory congruence. The resulting spatial-autoregressive tobit model of inter-state agricultural trade is estimated using a modified Expectation-Maximization algorithm. The empirical results show that the noxious weed regulatory congruence has a positive and significant effect on inter-state trade flows. Moreover, the inter-state trade distortion from consumer and commodity-producers lobbies is estimated to be as much as $1.1 billion. In the third essay, a leader-follower framework is used to examine when a weed species on one state's (leader) regulation is added to that of another (follower) state. For this purpose, an ordered logit model of noxious weeds' listing time is specified as a function of invader characteristics and ecosystem invasibility. The empirical results suggest that the invader status and attributes are relatively more important than ecosystem characteristics in determining the weed listing time. Together, the three essays suggest greater emphasis on the use of science than interest-group lobbying for listing noxious weeds. Moreover, a better documentation of potential invaders, their characteristics and impacts on non-native environments, is important in controlling the introduction and spread of noxious weeds, and the consequent economic and ecological damages. Title: Political economy and trade effects of invasive species regulation : the case of noxious weeds Author: Min, He Many non-native weed pests of food, fiber, and nursery crops pose threats to U.S. environment and agriculture. Noxious weed regulations play an important role in preventing the introduction and spread of non-native plants, thereby protecting the local biodiversity, environment and economic activities. However, these regulations could also hamper agricultural trade. The three essays of this dissertation address the causes and consequences of cross-state differences in noxious weed regulations. In the first essay, a political-economic model is developed to derive cross-state regulatory congruence as a function of ecological and agronomic characteristics, and interest-group lobbying through political contributions. Econometric estimation suggests ecological and agronomic dissimilarities are primary causes of cross-state differences in noxious weed regulation. However, evidence of lobbying effects is statistically and economically significant. In particular, agricultural seed producers favor more uniform weed regulations across states, while commodity producers and consumers prefer that their state maintain a distinct weed list to protect its ecosystem and agronomic conditions. The impact of noxious weed regulations on inter-state agricultural trade is measured in the second essay. In particular, the extent of trade distortions arising from interest-groups' lobbying is estimated. For this purpose, each state’s net trade in three industries - agricultural seeds, nursery products and commodities - is derived as a function of weed regulatory congruence. The resulting spatial-autoregressive tobit model of inter-state agricultural trade is estimated using a modified Expectation-Maximization algorithm. The empirical results show that the noxious weed regulatory congruence has a positive and significant effect on inter-state trade flows. Moreover, the inter-state trade distortion from consumer and commodity-producers lobbies is estimated to be as much as $1.1 billion. In the third essay, a leader-follower framework is used to examine when a weed species on one state's (leader) regulation is added to that of another (follower) state. For this purpose, an ordered logit model of noxious weeds' listing time is specified as a function of invader characteristics and ecosystem invasibility. The empirical results suggest that the invader status and attributes are relatively more important than ecosystem characteristics in determining the weed listing time. Together, the three essays suggest greater emphasis on the use of science than interest-group lobbying for listing noxious weeds. Moreover, a better documentation of potential invaders, their characteristics and impacts on non-native environments, is important in controlling the introduction and spread of noxious weeds, and the consequent economic and ecological damages. Close

• 355. [Article] Advancing marine reserve science : from field experiments to marine conservation planning tools

  This dissertation focuses on science relevant to the design and implementation of marine reserves. The chapters explore a range of topics related to among-site variation in population, community, and ecosystem ...

  Citation × Citation Citation Abstract Copy Title: Advancing marine reserve science : from field experiments to marine conservation planning tools Author: Leslie, Heather M. This dissertation focuses on science relevant to the design and implementation of marine reserves. The chapters explore a range of topics related to among-site variation in population, community, and ecosystem dynamics. My results demonstrate the value and feasibility of integrating this knowledge into more comprehensive conservation and management approaches. While the threats facing the oceans are serious, we in the scientific community have considerable information and tools to contribute to the development and implementation of solutions. In Chapter 2, I report on the effects of conspecific density on multiple traits of the intertidal barnacle Balanus glandula. The primary effects of increased density were enhanced survival and higher reproductive rates. My results provide a strategy for evaluating the relative importance of positive vs. negative intraspecific interactions when implementing reserves. In Chapter 3, my co-authors and I investigated how variation in nearshore primary productivity influenced survival, growth, and reproduction in B. glandula. We found strong evidence for bottom-up (i.e. productivity) forcing of barnacle population dynamics. One site produced substantially more larvae than the others, demonstrating the importance of among-site variability. Our findings advance understanding of bottom-up influences on marine populations, and demonstrate the value of embedding reserves within a network. In Chapter 4, my co-authors and I used benthic habitat data from the Florida Keys to show how a computer-based siting tool could be used to help design reserve networks. We found that many different combinations of sites produced satisfactory networks, and highlighted areas as potential conservation priorities. Our work was the first marine application of this tool and provided a starting point for applications in California and Australia. In Chapter 5, I report on a synthesis of marine conservation planning cases globally. I found that the majority occurred in North and Central America, were based on biogeographic boundaries, and that biodiversity conservation was the primary objective. One of the most striking findings was the paucity of well-documented cases. My results suggested that planners consider knowledge of marine populations, communities, and ecosystems important when identifying priorities, but that they do not have clear guidelines for how to integrate this information appropriately. Title: Advancing marine reserve science : from field experiments to marine conservation planning tools Author: Leslie, Heather M. This dissertation focuses on science relevant to the design and implementation of marine reserves. The chapters explore a range of topics related to among-site variation in population, community, and ecosystem dynamics. My results demonstrate the value and feasibility of integrating this knowledge into more comprehensive conservation and management approaches. While the threats facing the oceans are serious, we in the scientific community have considerable information and tools to contribute to the development and implementation of solutions. In Chapter 2, I report on the effects of conspecific density on multiple traits of the intertidal barnacle Balanus glandula. The primary effects of increased density were enhanced survival and higher reproductive rates. My results provide a strategy for evaluating the relative importance of positive vs. negative intraspecific interactions when implementing reserves. In Chapter 3, my co-authors and I investigated how variation in nearshore primary productivity influenced survival, growth, and reproduction in B. glandula. We found strong evidence for bottom-up (i.e. productivity) forcing of barnacle population dynamics. One site produced substantially more larvae than the others, demonstrating the importance of among-site variability. Our findings advance understanding of bottom-up influences on marine populations, and demonstrate the value of embedding reserves within a network. In Chapter 4, my co-authors and I used benthic habitat data from the Florida Keys to show how a computer-based siting tool could be used to help design reserve networks. We found that many different combinations of sites produced satisfactory networks, and highlighted areas as potential conservation priorities. Our work was the first marine application of this tool and provided a starting point for applications in California and Australia. In Chapter 5, I report on a synthesis of marine conservation planning cases globally. I found that the majority occurred in North and Central America, were based on biogeographic boundaries, and that biodiversity conservation was the primary objective. One of the most striking findings was the paucity of well-documented cases. My results suggested that planners consider knowledge of marine populations, communities, and ecosystems important when identifying priorities, but that they do not have clear guidelines for how to integrate this information appropriately. Close

• 356. [Article] Interactive effects of silvicultural herbicides and cervid herbivory on early seral plant communities of the northern Oregon Coast Range

  Intensive forest management (IFM, dense conifer plantings and herbicide applications) may alter the characteristics of early seral plant communities that function as major habitat resources for a host ...

  Citation × Citation Citation Abstract Copy Title: Interactive effects of silvicultural herbicides and cervid herbivory on early seral plant communities of the northern Oregon Coast Range Author: Stokely, Thomas Intensive forest management (IFM, dense conifer plantings and herbicide applications) may alter the characteristics of early seral plant communities that function as major habitat resources for a host of wildlife species, including cervid herbivores such as Cervus elaphus and Odocoileus hemionus. Such large herbivores can also substantially affect plant community characteristics and succession, especially in disturbed early seral habitats. I hypothesized that the effect of cervid herbivory on early seral plant communities is mediated by the effect of silvicultural herbicide treatments. If that is the case, intensively treated stands with low plant cover and diversity should be most susceptible to herbivory, as cervids are less selective and herbivory impacts are highly concentrated where forage has been diminished. To test this hypothesis, I experimentally established paired 225 m² cervid Exclusion and Open-Herbivory treatment plots in 28, 12-15 ha early seral plantation stands throughout the northern Oregon Coast Range, USA, representing a gradient in IFM. The gradient included three herbicide treatments and a no-spray Control applied at the stand scale and replicated using a randomized complete block design. I compared estimates of cover, height and diversity for entire plant communities and specific functional groups among herbivory and herbicide treatments using mixed-effects models with a blocked split-plot design. I found convincing evidence that the effect of herbivory was mediated by herbicide treatment. No-spray Control stands were too vigorous, diverse and rich with native perennial herb and deciduous shrub forage to be substantially impacted by cervid herbivory. The herbaceous specific, Light herbicide treatment reduced Shannon diversity and the cover and richness of native-perennial herbs, releasing deciduous shrub height growth where cervids where excluded. Highly selective herbivory suppressed the shrub height response by 20.5 cm, increasing the abundance and richness of introduced herb species. The broad spectrum, Moderate herbicide treatment reduced diversity, forage cover and diminished the cover and richness of deciduous shrubs and native-perennial herbs, favoring the dominance of introduced-ruderal herbs. Herbivory in the Moderate treatment reduced total cover by 17.7 percent cover, moderate-quality forage cover by 13.2 percent cover and native perennial herb richness by 1.5 species, while suppressing the cover of introduced-ruderal herbs by 4.58 percent cover and reducing the height of ferns and introduced-perennial herbs by 19.9 and 17.3 cm, respectively. Plant communities subject to the Heavy treatment were the most depauperate of all and herbivory exacerbated the effect of this treatment on native-perennial herbs only. Average height of dominant vegetation was consistently lower with cervid access across all stands, especially with Moderate herbicide treatment. My results provide evidence that by reducing diversity and the abundance of native forage species, herbicide treatments altered herbivory selectivity and pressure. The alteration of herbivory pressure in turn influenced the outcome of herbicide treatments, resulting in an exacerbated effect with Moderate and Heavy treatments. The effect of herbivory in controlling vegetation in managed stands may have positive implications for conifer seedling growth, constituting a possible 'ecosystem service' by cervids in the Pacific Northwest. This 'service' may be to the detriment of biodiversity and other early seral associates when coupled with common intensive forest management practices. Title: Interactive effects of silvicultural herbicides and cervid herbivory on early seral plant communities of the northern Oregon Coast Range Author: Stokely, Thomas Intensive forest management (IFM, dense conifer plantings and herbicide applications) may alter the characteristics of early seral plant communities that function as major habitat resources for a host of wildlife species, including cervid herbivores such as Cervus elaphus and Odocoileus hemionus. Such large herbivores can also substantially affect plant community characteristics and succession, especially in disturbed early seral habitats. I hypothesized that the effect of cervid herbivory on early seral plant communities is mediated by the effect of silvicultural herbicide treatments. If that is the case, intensively treated stands with low plant cover and diversity should be most susceptible to herbivory, as cervids are less selective and herbivory impacts are highly concentrated where forage has been diminished. To test this hypothesis, I experimentally established paired 225 m² cervid Exclusion and Open-Herbivory treatment plots in 28, 12-15 ha early seral plantation stands throughout the northern Oregon Coast Range, USA, representing a gradient in IFM. The gradient included three herbicide treatments and a no-spray Control applied at the stand scale and replicated using a randomized complete block design. I compared estimates of cover, height and diversity for entire plant communities and specific functional groups among herbivory and herbicide treatments using mixed-effects models with a blocked split-plot design. I found convincing evidence that the effect of herbivory was mediated by herbicide treatment. No-spray Control stands were too vigorous, diverse and rich with native perennial herb and deciduous shrub forage to be substantially impacted by cervid herbivory. The herbaceous specific, Light herbicide treatment reduced Shannon diversity and the cover and richness of native-perennial herbs, releasing deciduous shrub height growth where cervids where excluded. Highly selective herbivory suppressed the shrub height response by 20.5 cm, increasing the abundance and richness of introduced herb species. The broad spectrum, Moderate herbicide treatment reduced diversity, forage cover and diminished the cover and richness of deciduous shrubs and native-perennial herbs, favoring the dominance of introduced-ruderal herbs. Herbivory in the Moderate treatment reduced total cover by 17.7 percent cover, moderate-quality forage cover by 13.2 percent cover and native perennial herb richness by 1.5 species, while suppressing the cover of introduced-ruderal herbs by 4.58 percent cover and reducing the height of ferns and introduced-perennial herbs by 19.9 and 17.3 cm, respectively. Plant communities subject to the Heavy treatment were the most depauperate of all and herbivory exacerbated the effect of this treatment on native-perennial herbs only. Average height of dominant vegetation was consistently lower with cervid access across all stands, especially with Moderate herbicide treatment. My results provide evidence that by reducing diversity and the abundance of native forage species, herbicide treatments altered herbivory selectivity and pressure. The alteration of herbivory pressure in turn influenced the outcome of herbicide treatments, resulting in an exacerbated effect with Moderate and Heavy treatments. The effect of herbivory in controlling vegetation in managed stands may have positive implications for conifer seedling growth, constituting a possible 'ecosystem service' by cervids in the Pacific Northwest. This 'service' may be to the detriment of biodiversity and other early seral associates when coupled with common intensive forest management practices. Close

• 357. [Article] Connecting local values and forest policy to the international forest sustainability dialogue

  Sustainable management of the world’s forests is a key component for conserving biodiversity, soil and water resources, mitigating climate change, strengthening economies, and promoting sustainable communities ...

  Citation × Citation Citation Abstract Copy Title: Connecting local values and forest policy to the international forest sustainability dialogue Author: Morre, Susan K. Sustainable management of the world’s forests is a key component for conserving biodiversity, soil and water resources, mitigating climate change, strengthening economies, and promoting sustainable communities and human well-being, now and in the future. While international cooperation is important, the actual policies and management actions that affect forest conditions and trends are decided at the national and local level, and are influenced by local community values and individual attitudes toward natural resource management. It is important to understand the breadth of ways that people value forests if we want to sustain those specific forest values (benefits, products, and amenities) over time. I compared values identified in forest policies to values identified by individuals from six demographic groups in Oregon. The 2010 U.S. Census shows that Oregon is becoming more racially and ethnically diverse (U.S. Census Bureau 2011). The purpose of this research was to learn what forest values are most important to individuals from six demographic groups, are included in the policies and regulations that guide the management of Oregon’s forests, and in the international forest sustainability discussions. I triangulated qualitative data from multiple sources: previous literature; forest policy document analysis; participant observation of state, national, and international policy discussions; and 14 purposive focus groups with individuals from six racial and ethnic groups in Oregon. Data were individual words and language segments that expressed forest values. Analyses were conducted based on the Montreal Process Criteria and Indicators of Sustainable Forest Management (MPCI), a subset of those indicators and metrics that comprise the Oregon Indicators of Sustainable Forest Management, and focus group transcripts. The most common forest values expressed in the focus groups and previous national and state surveys that are currently included in the Oregon Indicators, Oregon forest policy documents and the MPCI are recreation, clean water, wood products, and economic values, including jobs, income, and revenues for public services. However, the current Oregon forest policies and indicator metrics do not include some forest values expressed in the focus groups and surveys: spiritual values, cultural heritage values, natural forest appearance, and protection of diverse native understory plants for wildlife habitat and cultural uses. The revised set of MPCI used in the 2010 and 2011 national reports includes indicators and metrics for understory plant and animal species diversity, as well as the new indicator 44 "the importance of forests to people" which is intended to capture these important spiritual and cultural values. I recommend revised Oregon Indicators, metrics, and forest policies to measure current conditions and trends of these values in Oregon's forests.  Title: Connecting local values and forest policy to the international forest sustainability dialogue Author: Morre, Susan K. Sustainable management of the world’s forests is a key component for conserving biodiversity, soil and water resources, mitigating climate change, strengthening economies, and promoting sustainable communities and human well-being, now and in the future. While international cooperation is important, the actual policies and management actions that affect forest conditions and trends are decided at the national and local level, and are influenced by local community values and individual attitudes toward natural resource management. It is important to understand the breadth of ways that people value forests if we want to sustain those specific forest values (benefits, products, and amenities) over time. I compared values identified in forest policies to values identified by individuals from six demographic groups in Oregon. The 2010 U.S. Census shows that Oregon is becoming more racially and ethnically diverse (U.S. Census Bureau 2011). The purpose of this research was to learn what forest values are most important to individuals from six demographic groups, are included in the policies and regulations that guide the management of Oregon’s forests, and in the international forest sustainability discussions. I triangulated qualitative data from multiple sources: previous literature; forest policy document analysis; participant observation of state, national, and international policy discussions; and 14 purposive focus groups with individuals from six racial and ethnic groups in Oregon. Data were individual words and language segments that expressed forest values. Analyses were conducted based on the Montreal Process Criteria and Indicators of Sustainable Forest Management (MPCI), a subset of those indicators and metrics that comprise the Oregon Indicators of Sustainable Forest Management, and focus group transcripts. The most common forest values expressed in the focus groups and previous national and state surveys that are currently included in the Oregon Indicators, Oregon forest policy documents and the MPCI are recreation, clean water, wood products, and economic values, including jobs, income, and revenues for public services. However, the current Oregon forest policies and indicator metrics do not include some forest values expressed in the focus groups and surveys: spiritual values, cultural heritage values, natural forest appearance, and protection of diverse native understory plants for wildlife habitat and cultural uses. The revised set of MPCI used in the 2010 and 2011 national reports includes indicators and metrics for understory plant and animal species diversity, as well as the new indicator 44 "the importance of forests to people" which is intended to capture these important spiritual and cultural values. I recommend revised Oregon Indicators, metrics, and forest policies to measure current conditions and trends of these values in Oregon's forests.  Close

• 358. [Article] Interactive visualization of diversity in multivariate data sets unified across fields of study

  The study of the diversity of multivariate objects shares common characteristics across disciplines, including ecology and organizational management. Nevertheless, experts in these two disciplines have ...

  Citation × Citation Citation Abstract Copy Title: Interactive visualization of diversity in multivariate data sets unified across fields of study Author: Pham, Tuan N. T. (Tuan Nguyen Tha) The study of the diversity of multivariate objects shares common characteristics across disciplines, including ecology and organizational management. Nevertheless, experts in these two disciplines have adopted somewhat separate diversity concepts and analysis techniques, limiting the ability of potentially sharing and cross comparing these concerns. Moreover, while complex diversity data may benefit from exploratory data analysis, most of the existing techniques emphasize confirmatory analysis based on statistical metrics and models. To bridge these gaps, interactive visualization is especially appealing because of its potential to allow users to explore diversity data in a direct and holistic way, prior to further statistical analysis. This dissertation addresses the problem of designing multivariate visualizations that support exploration and communication of diversity patterns and processes in multivariate data. To this aim, the dissertation presents design considerations as well as implementation and evaluation of interactive visualizations targeting diversity analysis. The contributing visualization techniques and tools include (1) Diversity Map -- a novel multivariate space-filling representation emphasizing diversity patterns in separate attributes; (2) Ecological Distributions and Trends Explorer (EcoDATE) -- a web-based visual-analysis tool that is built upon the Diversity Map and facilitates the exploratory analysis of long-term ecological data with an emphasis on distribution patterns and temporal trends; and (3) HIST -- a visual representation for communicating team diversity faultlines across multiple attributes that is based on multiple linked, stacked histograms. Further, drawing upon lessons from these designs, this dissertation cross compares analyses of species diversity (ecology), microbial diversity (microbiology), and workgroup diversity (organizational management) and introduces a unified taxonomy of analytical tasks to guide the creation and evaluation of future diversity visualizations. The design considerations, visualization techniques, tools, and task taxonomy are evaluated and refined in empirical user studies involving human participants and subject-matter experts. Title: Interactive visualization of diversity in multivariate data sets unified across fields of study Author: Pham, Tuan N. T. (Tuan Nguyen Tha) The study of the diversity of multivariate objects shares common characteristics across disciplines, including ecology and organizational management. Nevertheless, experts in these two disciplines have adopted somewhat separate diversity concepts and analysis techniques, limiting the ability of potentially sharing and cross comparing these concerns. Moreover, while complex diversity data may benefit from exploratory data analysis, most of the existing techniques emphasize confirmatory analysis based on statistical metrics and models. To bridge these gaps, interactive visualization is especially appealing because of its potential to allow users to explore diversity data in a direct and holistic way, prior to further statistical analysis. This dissertation addresses the problem of designing multivariate visualizations that support exploration and communication of diversity patterns and processes in multivariate data. To this aim, the dissertation presents design considerations as well as implementation and evaluation of interactive visualizations targeting diversity analysis. The contributing visualization techniques and tools include (1) Diversity Map -- a novel multivariate space-filling representation emphasizing diversity patterns in separate attributes; (2) Ecological Distributions and Trends Explorer (EcoDATE) -- a web-based visual-analysis tool that is built upon the Diversity Map and facilitates the exploratory analysis of long-term ecological data with an emphasis on distribution patterns and temporal trends; and (3) HIST -- a visual representation for communicating team diversity faultlines across multiple attributes that is based on multiple linked, stacked histograms. Further, drawing upon lessons from these designs, this dissertation cross compares analyses of species diversity (ecology), microbial diversity (microbiology), and workgroup diversity (organizational management) and introduces a unified taxonomy of analytical tasks to guide the creation and evaluation of future diversity visualizations. The design considerations, visualization techniques, tools, and task taxonomy are evaluated and refined in empirical user studies involving human participants and subject-matter experts. Close

• 359. [Article] Environmental influences on host-pathogen dynamics of the amphibian chytrid fungus

  The causes of the global biodiversity crisis are varied and complex. Anthropogenic threats may act in isolation, or interact additively or synergistically with each other or with natural stressors to affect ...

  Citation × Citation Citation Abstract Copy Title: Environmental influences on host-pathogen dynamics of the amphibian chytrid fungus Author: Buck, Julia C. The causes of the global biodiversity crisis are varied and complex. Anthropogenic threats may act in isolation, or interact additively or synergistically with each other or with natural stressors to affect sensitive taxa. The recent emergence of many infectious diseases in wildlife has brought attention to the role of disease in population declines and species extinctions. Both abiotic and biotic components of the environment may mitigate or exacerbate effects of pathogens on their hosts through direct or indirect mechanisms. The effects of the environment on host-pathogen dynamics are complex, context-dependent, and in need of further examination. One particularly sensitive group, amphibians, is at the leading edge of the sixth mass extinction. The emerging infectious disease (EID) chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatis (Bd), is implicated in population declines and extinctions of amphibians globally. My disseration addresses questions pertaining to environmental influences on disease dynamics of Bd. As described in chapter 1, various abiotic and biotic components of the environment may affect host-pathogen dynamics of Bd, resulting in changes to the dynamics of Bd transmission and spread. Chapter 2 examines the influence of an abiotic factor, the insecticide (carbaryl) and three different assemblages of larval Pacific treefrogs (Pseudacris regilla) and Cascades frogs (Rana cascadae) on host-pathogen dynamics of Bd within a community context. I found separate effects of each treatment on amphibian growth and development, but no interactive effects among the treatments. However, Bd appeared to reduce phytoplankton abundance and increase periphyton biomass, an unexpected result that merited further investigation. One possible explanation for the results described in chapter 2 is that zooplankton might consume Bd zoospores, the infective stage of the pathogen, a hypothesis that I examine in chapter 3. I conducted laboratory experiments and confirmed the presence of Bd zoospores in the gut of Daphnia sp. through quantitative PCR and visual inspection. I discuss conservation implications of this finding. To determine whether predation on Bd zoospores by zooplankton could reduce infection in amphibians, I conducted a mesocosm experiment, which is described in chapter 4. I found complex effects on species interactions: competition between larval Cascades frogs and zooplankton for phytoplankton resources reduced phytoplankton concentration, zooplankton abundance, and survival of amphibians. These effects were diminished in the presence of Bd, suggesting that zooplankton may have at least partially substituted Bd zoospores for phytoplankton in their diet, thus stimulating competitive release. However, competitive effects between zooplankton and larval amphibians overshadowed indirect positive benefits of zooplankton predation on Bd zoospores. In chapter 4, competitive effects between zooplankton and larval amphibians for phytoplankton suggested that host-pathogen dynamics might be affected by the host’s supply of resources. Chapter 5 describes a mesocosm experiment that examined how eutrophication might affect Bd-infected Pacific treefrogs and other members of the aquatic community. Nutrient additions caused increased algal growth, which benefitted herbivorous larval amphibians. Larvae exposed to Bd altered their growth, development, and diet, and allocated resources differently than unexposed individuals. However, nutrient supplementation did not alter the response of larval amphibians to Bd. As described in chapter 6, consideration of hosts and pathogens as functional members of the ecological communities in which they exist can lead to important insights in host-pathogen dynamics. My PhD research may contribute to control measures for the emerging infectious disease chytridiomycosis. Title: Environmental influences on host-pathogen dynamics of the amphibian chytrid fungus Author: Buck, Julia C. The causes of the global biodiversity crisis are varied and complex. Anthropogenic threats may act in isolation, or interact additively or synergistically with each other or with natural stressors to affect sensitive taxa. The recent emergence of many infectious diseases in wildlife has brought attention to the role of disease in population declines and species extinctions. Both abiotic and biotic components of the environment may mitigate or exacerbate effects of pathogens on their hosts through direct or indirect mechanisms. The effects of the environment on host-pathogen dynamics are complex, context-dependent, and in need of further examination. One particularly sensitive group, amphibians, is at the leading edge of the sixth mass extinction. The emerging infectious disease (EID) chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatis (Bd), is implicated in population declines and extinctions of amphibians globally. My disseration addresses questions pertaining to environmental influences on disease dynamics of Bd. As described in chapter 1, various abiotic and biotic components of the environment may affect host-pathogen dynamics of Bd, resulting in changes to the dynamics of Bd transmission and spread. Chapter 2 examines the influence of an abiotic factor, the insecticide (carbaryl) and three different assemblages of larval Pacific treefrogs (Pseudacris regilla) and Cascades frogs (Rana cascadae) on host-pathogen dynamics of Bd within a community context. I found separate effects of each treatment on amphibian growth and development, but no interactive effects among the treatments. However, Bd appeared to reduce phytoplankton abundance and increase periphyton biomass, an unexpected result that merited further investigation. One possible explanation for the results described in chapter 2 is that zooplankton might consume Bd zoospores, the infective stage of the pathogen, a hypothesis that I examine in chapter 3. I conducted laboratory experiments and confirmed the presence of Bd zoospores in the gut of Daphnia sp. through quantitative PCR and visual inspection. I discuss conservation implications of this finding. To determine whether predation on Bd zoospores by zooplankton could reduce infection in amphibians, I conducted a mesocosm experiment, which is described in chapter 4. I found complex effects on species interactions: competition between larval Cascades frogs and zooplankton for phytoplankton resources reduced phytoplankton concentration, zooplankton abundance, and survival of amphibians. These effects were diminished in the presence of Bd, suggesting that zooplankton may have at least partially substituted Bd zoospores for phytoplankton in their diet, thus stimulating competitive release. However, competitive effects between zooplankton and larval amphibians overshadowed indirect positive benefits of zooplankton predation on Bd zoospores. In chapter 4, competitive effects between zooplankton and larval amphibians for phytoplankton suggested that host-pathogen dynamics might be affected by the host’s supply of resources. Chapter 5 describes a mesocosm experiment that examined how eutrophication might affect Bd-infected Pacific treefrogs and other members of the aquatic community. Nutrient additions caused increased algal growth, which benefitted herbivorous larval amphibians. Larvae exposed to Bd altered their growth, development, and diet, and allocated resources differently than unexposed individuals. However, nutrient supplementation did not alter the response of larval amphibians to Bd. As described in chapter 6, consideration of hosts and pathogens as functional members of the ecological communities in which they exist can lead to important insights in host-pathogen dynamics. My PhD research may contribute to control measures for the emerging infectious disease chytridiomycosis. Close

• 360. [Article] Aquatic community responses to drought disturbance: experimental manipulations of top predator extinctions and stream drying

  Although it is generally assumed that the intensifying abiotic environment is the primary effect of drought on aquatic organisms, drought-induced top predator extinctions may be an important underlying ...

  Citation × Citation Citation Abstract Copy Title: Aquatic community responses to drought disturbance: experimental manipulations of top predator extinctions and stream drying Author: Boersma, Kate S. Although it is generally assumed that the intensifying abiotic environment is the primary effect of drought on aquatic organisms, drought-induced top predator extinctions may be an important underlying mechanism. I used manipulative experiments to disentangle the impacts of drying and top predator extinctions on arid-land aquatic invertebrate communities. I then created a general conceptual framework that specifies how biotic and abiotic disturbances affect the composition of biological traits of species in a community (functional trait composition) and tested the framework with data from the manipulative experiments and a field study. Finally, I proposed a new metric to calculate the difference in functional trait composition between undisturbed and disturbed communities (called “functional distance”) and used it to understand trait turnover between undisturbed and disturbed arid-land stream communities. In Chapter 2, I describe two manipulative experiments in which I removed an invertebrate top predator from mesocosms containing arid-land stream invertebrates and recorded changes in the aquatic community. I found that top predator removal consistently decreased the abundance of detritivores and increased the abundance of mesopredators, even under different background environmental conditions. Chapter 3 describes a second mesocosm study in which I manipulated drying severity and measured aquatic community responses. My severe drying treatment allowed mesocosms to desiccate to a depth of ~1cm, yet I still I found that taxonomic and functional trait composition did not vary between treatments. The only discernable effect of drying was a decrease in abundance and increase in density of invertebrates. This result suggests that arid-land aquatic communities are highly resistant to drying disturbance that falls within the range of natural seasonal and interannual droughts but not resistant to the novel disturbance of top predator extinctions. In Chapter 4 I describe a conceptual framework that uses functional trait diversity to understand the mechanisms behind community responses to disturbances. I applied the framework to datasets from Chapters 2 and 3 and an observational field study during severe drought. While the biotic disturbance of top predator removal did not affect species diversity in the taxonomic analysis, it increased the overall functional trait diversity and favored trait combinations associated with aerial dispersal and predatory feeding modes. Interestingly, although natural stream drying occurred concurrently with the local extinction of the invertebrate top predator in the field, this extreme abiotic disturbance was associated with a reduction in functional trait diversity. The contradictory effects of these two novel disturbance types highlight the importance of colonization and spatial context in the resilience of arid-land aquatic communities to future disturbances; differences between disturbed and undisturbed communities in both top predator removal and catastrophic stream drying studies were associated with aerially dispersing invertebrates. My work suggests that combining taxonomic and functional trait analyses in a rigorous hypothesis-testing framework can reveal hidden mechanisms behind the effects of drought on aquatic communities. Ultimately, I hope that this framework can be applied to other disturbed systems to better understand the effects of human actions on ecological communities. Title: Aquatic community responses to drought disturbance: experimental manipulations of top predator extinctions and stream drying Author: Boersma, Kate S. Although it is generally assumed that the intensifying abiotic environment is the primary effect of drought on aquatic organisms, drought-induced top predator extinctions may be an important underlying mechanism. I used manipulative experiments to disentangle the impacts of drying and top predator extinctions on arid-land aquatic invertebrate communities. I then created a general conceptual framework that specifies how biotic and abiotic disturbances affect the composition of biological traits of species in a community (functional trait composition) and tested the framework with data from the manipulative experiments and a field study. Finally, I proposed a new metric to calculate the difference in functional trait composition between undisturbed and disturbed communities (called “functional distance”) and used it to understand trait turnover between undisturbed and disturbed arid-land stream communities. In Chapter 2, I describe two manipulative experiments in which I removed an invertebrate top predator from mesocosms containing arid-land stream invertebrates and recorded changes in the aquatic community. I found that top predator removal consistently decreased the abundance of detritivores and increased the abundance of mesopredators, even under different background environmental conditions. Chapter 3 describes a second mesocosm study in which I manipulated drying severity and measured aquatic community responses. My severe drying treatment allowed mesocosms to desiccate to a depth of ~1cm, yet I still I found that taxonomic and functional trait composition did not vary between treatments. The only discernable effect of drying was a decrease in abundance and increase in density of invertebrates. This result suggests that arid-land aquatic communities are highly resistant to drying disturbance that falls within the range of natural seasonal and interannual droughts but not resistant to the novel disturbance of top predator extinctions. In Chapter 4 I describe a conceptual framework that uses functional trait diversity to understand the mechanisms behind community responses to disturbances. I applied the framework to datasets from Chapters 2 and 3 and an observational field study during severe drought. While the biotic disturbance of top predator removal did not affect species diversity in the taxonomic analysis, it increased the overall functional trait diversity and favored trait combinations associated with aerial dispersal and predatory feeding modes. Interestingly, although natural stream drying occurred concurrently with the local extinction of the invertebrate top predator in the field, this extreme abiotic disturbance was associated with a reduction in functional trait diversity. The contradictory effects of these two novel disturbance types highlight the importance of colonization and spatial context in the resilience of arid-land aquatic communities to future disturbances; differences between disturbed and undisturbed communities in both top predator removal and catastrophic stream drying studies were associated with aerially dispersing invertebrates. My work suggests that combining taxonomic and functional trait analyses in a rigorous hypothesis-testing framework can reveal hidden mechanisms behind the effects of drought on aquatic communities. Ultimately, I hope that this framework can be applied to other disturbed systems to better understand the effects of human actions on ecological communities. Close