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xiv, 166 p. : ill. A print copy of this title is available through the UO Libraries. Search the library catalog for the location and call number.
Citation Citation
- Title:
- Community and ecosystem dynamics in remnant and restored prairies
- Author:
- Pfeifer-Meister, Laurel, 1978-
- Year:
- 2009, 2008
xiv, 166 p. : ill. A print copy of this title is available through the UO Libraries. Search the library catalog for the location and call number.
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2. [Article] The Schultz Fire : an interdisciplinary perspective on its history, management, and ecological effects
This thesis examines the Schultz Fire as a case study to explain the complex history of fire suppression management in America’s forests, and to gain further understanding of how management practices have ...Citation Citation
- Title:
- The Schultz Fire : an interdisciplinary perspective on its history, management, and ecological effects
- Author:
- Ranseen, Susanne N.
This thesis examines the Schultz Fire as a case study to explain the complex history of fire suppression management in America’s forests, and to gain further understanding of how management practices have affected the increase in fire severity levels and how forests respond to such a disturbance. The thesis objectives were: (1) to analyze the causes of the fire severity of the Schultz Fire, especially: topography, fuels, or weather; (2); to examine the possible correlation between fire severity and tree density; (3) to investigate whether post-fire species richness was related to fire severity two years after the Schultz Fire; (4) to investigate whether post-fire plant species richness, plant cover, and tree regeneration was related to fire severity two years after the Schultz Fire; and (5) to interlink and convey how these factors relate to the history of fire management and policy and public perception. The history of fire related policy and management has significantly changed the dynamics of America's national parks and forests. Understanding the larger context of this history, both of national fire management and of the effects of language and perception on policy and public reaction, is part of understanding the Schultz Fire as a whole. Based on modeling, high winds combined with the presence of high surface fuel load were the main causes of the Schultz Fire's high fire severity levels. As fire severity increased there was a statistically significant increase in species richness. Severity level had little variation on percentage of cover by plants. No statistically significant relationship between tree density and fire severity levels was found. These findings underline the need for fuel treatments in southwest Ponderosa Pine forests, and effective cooperation between communities, managers, and ecologists. The Schultz Fire serves as an example in understanding the intricacies of how history affects the present and future of fire management. How fire has been managed and portrayed in the past has left an indelible mark on how fire is presently viewed. Without a clear understanding of the history of fire management and the role of fire in the ecology, future policies towards fire will be unable to account for and manage for the diversity of ecosystems and fires effects on those ecosystems across the United States.
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3. [Article] Predictability and Constraints on the Structure of Ecological Communities in the Context of Climate Change
Ecologists must increasingly balance the need for accurate predictions about how ecosystems will be affected by climate change, against the fact that making such predictions at the ecosystem-level may ...Citation Citation
- Title:
- Predictability and Constraints on the Structure of Ecological Communities in the Context of Climate Change
- Author:
- Barner, Allison K.
Ecologists must increasingly balance the need for accurate predictions about how ecosystems will be affected by climate change, against the fact that making such predictions at the ecosystem-level may be infeasible. Although information about responses of individual species to a changing environment is increasing, scaling such information to the community level is challenging. To date, predicting responses of ecological communities to climate change is constrained by limited theoretical and empirical knowledge about the response of communities and ecosystems to change. My dissertation addresses several knowledge gaps in our understanding of community structure under climate change. This research draws from a rich experimental tradition in the species-diverse model ecosystem of the US Pacific Northwest rocky intertidal to test ecological theory. In Chapter 2, I assessed whether the response of multiple species of coralline algae to global change could be predicted from basic first principles of chemistry, physiology, and ecology. Given the rate of global change, and the time-consuming process of experimentally determining species responses to climate change, I hypothesized that species can be grouped using existing theory, either by their evolutionary relatedness or by their ecological traits, such that climate responses are similar within a group. Such a scheme would greatly reduce the number of experiments needed to characterize species climate vulnerability, requiring the characterization of the response of groups of species to climate change, rather than individual species. Using a suite of five co-occurring species of intertidal articulated coralline algae (Corallina vancouveriensis, Corallina officinalis, Bossiella plumosa, Bossiella orbiginiana, and Calliarthron tuberculosum), I applied this framework to generate ten mutually exclusive hypotheses that could explain organismal response to ocean acidification, a consequence of global climate change that threatens marine calcifying species. I found that all species had similar responses to ocean acidification, and that responses were generally predicted by the body size of the individual. Despite the power that such a framework provides in understanding group-level response to climate change, predicting community-level response requires knowledge of how organisms affect one another. In Chapter 3, I quantified species interactions in a series of removal experiments to estimate the reciprocal effects between a canopy-forming intertidal kelp (Saccharina sessilis) and a suite of understory species that persist beneath the kelp canopy. This experiment was replicated in different oceanographic conditions across a large latitudinal gradient, as a step towards understanding how interactions might change with climate change. However, the experiment demonstrated that interactions between the canopy and understory were consistent among different environmental conditions. Furthermore, the strongest effect was that of understory species, particularly articulated coralline turf algae, on the canopy species. The coralline turf algae both facilitated the recruitment of the canopy species and buffered the canopy from abiotic stress during its adult life stage. Combining experimental results and observational surveys, a hypothesized interaction network for these species was constructed, highlighting the importance of direct and indirect species interactions in promoting species coexistence. A long-standing controversy in ecology is whether or not species interactions can be inferred from observational data, as opposed to from experimental tests. Although the rocky intertidal ecosystem is unique for its ease of experimental manipulation, quantifying species interactions experimentally is often difficult or impossible. As an alternative, many have turned to statistical methods to estimate species interactions from observational data, namely, from patterns in species pairwise co-occurrences. In Chapter 4, I examined these co-occurrence methods and their potential relationship to experimentally measured species interactions. I first used a suite of different co-occurrence methods to generate a set of predicted species interactions of macrophytes and invertebrates from observational surveys conducted in the rocky intertidal zone of Oregon. I then compared the predicted species interactions to the same pairwise species interactions determined experimentally and assembled from the literature. Overall, of the seven methods tested, each generated a different set of predicted species interactions from the same data, and all methods predicted interactions that did not match those in the experimental database. Thus, predicting species interactions from patterns in occurrence remains elusive. Importantly, much work remains to be done to understand the link between species co-occurrences and their actual interactions with one another on the landscape. A key limiting frontier in climate change ecology is determining the influence of species interactions on species distributions across the landscape, and the sensitivity of such interactions to changes in climate. Finally, in Chapter 5, I used theory from the published literature and knowledge from my previous chapters to make predictions the recovery of low rocky intertidal communities after a disturbance. The process of community development after disturbance has been studied in many ways, from the successional studies of the early 1900s, to modern community assembly theory. In recent years, a focus on the unpredictability of community assembly has emerged, paying particular attention to the role of historical contingency, or priority effects, in determining the recovery trajectory of a community. Priority effects occur when the arrival of a species after a disturbance inalterably changes the composition of the developing community, driving the assembly of widely different communities at a small spatial scale. I conducted a community assembly experiment in three different low intertidal zone community "types", each characterized by different dominant macrophyte species (Saccharina sessilis, Phyllospadix spp., and algal "turfs"). Replicating this experiment at six sites along the Oregon coast, I found that both regional and local dynamics constrain the recovery of communities after disturbance. Half of the time, the community returned to the state of the nearby community type. The remaining communities were influenced by priority effects that could be predicted based on 1) regional dynamics favoring some species over others, or 2) the timing of arrival of important facilitating species. Overall, understanding the dynamic relationship between the persistence of diverse communities and a changing environment remains one of the challenges of our time. My dissertation highlights some of the challenges in predicting the future composition of communities under climate change, but also provides some ways forward. Integration of experimental, theoretical, and observational studies builds the scaffolding of prediction, whereby understanding the constraints on species physiology, the interactions among species, and community assembly can help frame the context in which predictions are made.
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4. [Article] Increased Taxonomic and Functional Similarity Does Not Increase the Trophic Similarity of Communities
Aim: Despite a long-standing research interest in the association between the biodiversity (i.e. taxonomic and functional composition) and trophic structure of communities, our understanding of the relationship ...Citation Citation
- Title:
- Increased Taxonomic and Functional Similarity Does Not Increase the Trophic Similarity of Communities
- Author:
- Pool, Thomas K., Cucherousset, Julien, Boulêtreau, Stéphanie, Villéger, Sébastien, Strecker, Angela L., Grenouillet, Gaël
- Year:
- 2015
Aim: Despite a long-standing research interest in the association between the biodiversity (i.e. taxonomic and functional composition) and trophic structure of communities, our understanding of the relationship remains limited. Community assembly theory predicts that niche partitioning will result in communities with a diverse array of functional traits, which in turn may facilitate a correspondingly diverse array of trophic interactions that define the trophic niche of those communities. The aim of our study is to test this prediction. Methods: We built a database composed of functional traits and stable isotope values (δ13C and δ15N) for 63 freshwater fish communities containing 109 species in 34 lentic and 29 lotic ecosystems. First, using linear mixed models (i.e. an alpha-diversity approach), we tested whether the taxonomic diversity of communities was positively associated with their functional diversity and if their functional diversity was positively associated with their trophic diversity. Second, we assessed the taxonomic, functional and trophic similarity of communities using multiple regression on distance matrices (MRM) and their respective ‘turnover’ and ‘nestedness-resultant’ components to test if the taxonomic similarity of communities was positively correlated with their functional similarity and if their functional similarity was positively associated with their trophic similarity (i.e. a beta-diversity approach). Results: We found that the functional diversity of communities increased as their taxonomic diversity increased. Similarly, the trophic diversity of communities increased as their functional diversity increased. The pairwise taxonomic and functional similarity of communities were also positively associated, but there was a weak relationship between the functional and trophic similarities of communities. Main conclusions: Our study demonstrates that communities with similar functional characteristics can have disparate food web structures, suggesting that additional site-specific factors influence community variation in trophic niche geometry. Determining the relative importance of functional characteristics and site-specific factors in shaping trophic interactions is crucial for a better understanding of how future species loss and species introductions will affect food web structure and ecosystem functioning.
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Predators are fundamentally important for regulating and driving prey population dynamics as well as structuring ecological communities. Over-exploitation of marine resources has caused dramatic depletions ...
Citation Citation
- Title:
- Indirect effects of fishing on predators and their prey
- Author:
- Stallings, Christopher Derek
Predators are fundamentally important for regulating and driving prey population dynamics as well as structuring ecological communities. Over-exploitation of marine resources has caused dramatic depletions of predatory fish species and shifts in marine community composition, with attendant declines in productivity and diversity of marine ecosystems. Despite the important ramifications of these patterns for humankind, the specific ecological mechanisms and potential indirect effects underlying these trends have been largely unexplored. I combined small-scale experiments and broad-scale observations to investigate how fishing can affect interactions among predators and subsequently be transferred to interactions between predators and their prey. Previous observations had indicated that small, unfished predators increase in abundance on reefs where large, fished predators are removed. To test the effects of such shifts in relative abundance of different predatory fishes on community structure of lower trophic-level species, I manipulated the presence of fished and unfished predatory species on coral patch reefs in the Bahamas. This controlled field experiment demonstrated that different predatory fishes, which are often assumed to have similar effects on prey species, in fact had remarkably different effects on prey diversity and abundance. In a second field experiment, I found that increased abundance of a large, fished predatory species on coral reefs decreased the activity and growth of smaller, unfished predators. Although small, unfished predators had strong, negative effects on lower trophic-level prey on reefs with low abundances of larger, fished predators, these effects were reduced with increasing abundance of the fished species. Lastly, I used observational data from volunteer SCUBA-diver surveys to investigate how the structure of predatory fish communities on coral reefs across the greater Caribbean region has been affected by fishing. I used density of human populations as a proxy for fishing intensity. I found that, as human density increases, overall predator abundance and diversity decreases, and reef communities became dominated by only a few, small species. This research indicates that the effects of fishing on larger predatory species can permeate throughout ecological communities, well beyond simple reductions in the abundance of fished species. In light of these community-wide effects, ecosystem-based approaches are necessary for successful management of fisheries and conservation of coral reefs.
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As species of ash trees become increasingly threatened worldwide by exotic pests and pathogens, it is important to develop descriptions of their ecologies that help guide the conservation and restoration ...
Citation Citation
- Title:
- Overstory Structure and Community Characteristics of Oregon Ash (Fraxinus latifolia) Forests of the Willamette Valley, Oregon
- Author:
- Prive, Sean
As species of ash trees become increasingly threatened worldwide by exotic pests and pathogens, it is important to develop descriptions of their ecologies that help guide the conservation and restoration of forests in which they are a major component. Oregon ash (Fraxinus latifolia) is a dominant tree species in wetland forests of the Willamette Valley, Oregon. It is potentially threatened by the emerald ash borer, an exotic forest insect that is expanding in range in North America. The arrival of the emerald ash borer in the western United States is expected to cause high rates of Oregon ash mortality, which will likely highly alter structural and compositional characteristics of regional riparian and wetland forests. To investigate the structural development and plant community dynamics of Willamette Valley Oregon ash forests, I quantified species structure and composition for both overstory and understory communities along gradients of stand age and soil moisture. Community Type Wetland Index (CTWI) scores were calculated for each plot by multiplying plot-level species abundances by the national wetland indicator value for each species, and were used as an approximation of local soil moisture regimes. Ash forests and early seral savannas were sampled in 102 plots within 11 wetlands between Lane and Washington Counties, Oregon. Early seral wetland savannas were dominated by herbaceous vegetation and had highly variable ash and other tree species recruitment. Young ash forests initiated on wetland sites that were formally maintained as savannas via anthropogenic disturbance. Structural development in these forests generally followed previously described post-disturbance stages: stem exclusion, understory initiation, young multi-strata, and old growth. As stands aged, tree densities decreased and mean tree diameter increased. Mean stand densities (for trees >5 cm at 1.3 m height) ranged from 1727 trees per hectare in stem exclusion stands to 348 in old growth stands, while mean tree diameter increased from 12 to 32 cm between those same stages. Furthermore, understory vegetation shifted from herbaceous to shrub and understory tree species. Oregon ash had the greatest relative dominance of all tree species at all stages of structural development. Oregon white oak (Quercus garryana) was the only other tree species commonly found in forest canopies, though it was typically far less abundant than Oregon ash. Plots in which oak was present had a greater depth to soil mottling, indicating a lower depth to the annual high water table. Oregon ash was also the most commonly regenerating tree species in all stages of structural development, and nearly 70% of ash regeneration was vegetative. Other tree regeneration was typically restricted to understory species, especially cascara (Rhamnus purshiana) in forests and hawthorn (Crataegus spp.) in savannas. Forest structural diversity increased between each stage of development. In total, 216 plant species were identified. Of these, 147 were found in forest plots. Community composition differed significantly between forests and savannas, and between "young" (stem exclusion and understory initiation) plots and "old" (young multi-strata and old growth) plots. Nonmetric multidimensional scaling (NMS) indicated that, for all wetland plots, the environmental variables most highly correlated with community composition were CTWI scores and canopy cover. For forest plots only, NMS indicated that CTWI scores and stand density were the environmental variables most related to patterns in community composition. Species richness was not correlated with canopy cover, but was negatively correlated with CTWI scores. Exotic species cover was negatively correlated with canopy cover, but was not correlated with CTWI scores. Exotic species composition was dependent on both canopy cover and CTWI scores. On wet sites, reed canary grass (Phalaris arundinacea) was particularly abundant, and was associated with low species richness. On drier sites, common exotic species included trees and shrubs such as blackberries (Rubus spp.), exotic roses (Rosa spp.), single-seeded hawthorn (Crataegus monogyna), and common pear (Pyrus communis) as well as several grass and forb species. The results of this study suggest that, although overstory tree communities are characterized by low diversity, Oregon ash forests are important for landscape-scale structural and plant community diversity in Willamette Valley wetlands. However, overstory tree communities lack diversity; Oregon ash appears to be both an early seral, colonizing species in open wetlands and a climax species that is capable of regenerating under a closed canopy. Few other trees are present regionally that are capable of maintaining a forested state in wetlands. Furthermore, closed canopy Oregon ash forests may suppress exotic species spread, and in the absence of management, overstory ash mortality may lead to increased exotic plant cover. Regardless of future forest health threats, intact Oregon ash forests, like other regional wetland-types, are currently few and limited in extent and should be considered a conservation priority.
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I focus on addressing knowledge gaps relating to management of cryptogams in Oregon's public lands in Pseudotsuga menziesii-Tsuga heterophylla forests on the west side of the Cascade Range and dryland ...
Citation Citation
- Title:
- Cryptogam communities in forest and steppe ecosystems of Oregon, USA
- Author:
- Root, Heather T.
I focus on addressing knowledge gaps relating to management of cryptogams in Oregon's public lands in Pseudotsuga menziesii-Tsuga heterophylla forests on the west side of the Cascade Range and dryland steppe in the Cascade Range's rainshadow. While a great deal of research has illustrated the importance of late-successional forests for maintaining biodiversity in the Pacific Northwest of North America, over 76% of the forests in the region are less than 100 years old. To preserve landscape-level biodiversity, forest managers are increasingly interested in how young stands can be manipulated to favor late-successional species. At two sites in moist conifer forests of western Oregon, lichen community monitoring plots were established prior to treatment and resampled approximately 10 years after alternative thinning treatments aimed at promoting late-successional strucural characteristics. At both sites, hardwood gaps and open-grown trees were positively associated with cyanolichen species richness. At one site, thinned plots hosted more Bryoria, Candelaria concolor, Leptogium polycarpum, Peltigera collina, Nephroma laevigatum and Physcia tenella than had been observed prior to thinning. I concluded that thinning treatments retaining remnants, open-grown trees and hardwood gaps have potential to favor lichen communities rich in cyanolichen and alectorioid species. In the same sites, I sought to understand how stand-level gradients in canopy structure relate to dominant forest floor bryophyte and lichen species composition and abundance. At the one site, I found no strong associations between forest floor communities and stand structural characteristics. At the the other, lichens, particularly Cladonia, were negatively associated with canopy cover whereas bryophyte abundance was positively associated with Tsuga basal area. This relationship was stronger in the thinned stands, which had a different community composition than those left unthinned. Overall, the forest floor communities were fairly homogeneous at both sites and relationships with stand structural variables were subtle, indicating that thinning did not have a strong impact. Biological soil crusts are ecosystem engineers in arid and semi-arid habitats; they affect soil chemistry, stability, and vegetation. Little is known about regional variation in biotic crust communities of North America. I explored how biotic crust lichen community composition and richness related to vascular plant, soil and climate characteristics in Oregon. In 59 0.4-ha plots, I found 99 biotic crust lichen taxa, one-third of which were observed only once, 33 of which occurred in only one plot and seven of which were new to Oregon. I compiled records from herbaria and other studies to evaluate the rarity of 124 biotic crust lichen species and conclude that 37 are rare or uncommon. Many of these appear to be associated with calcareous substrates. I modeled occurrences in relation to climate and soil variables for four uncommon biotic crust lichens: Acarospora schleicheri, Fuscopannaria cyanolepra, Rhizocarpon diploschistidina, and Texosporium sancti-jacobi. Based on climate and soils, I mapped regions of Oregon that may support new populations of these species and overlay habitats unsuitable for biotic crusts due to development and agriculture. These species, except Fuscopannaria cyanolepra, are strongly associated with the fine soils along the Columbia and Treasure Valleys that are most intensively used for agriculture. Biotic crust lichen communities rich in cyanolichens characterized Juniperus stands whereas warm grasslands were home to regionally uncommon species including Texosporium sancti-jacobi and Rhizocarpon diploschistidina. I discerned biotic crust communities in sandy Artemisia tridentata ssp. wyomingensis sites from those loamy A. arbuscula sites. Hotspots of biotic crust diversity were geographically scattered, weakly negatively associated with abundance of shrubs of disturbed sites, Gutierrezia and Chrysothamnus. The poorest sites for biotic crust lichen richness were heavily grazed, burned plots with Gutierrezia in the grassy north, unstable steep talus slopes at the center, and sandy, grazed sites with Chrysothamnus in the southern portion of our region. Overall, regional patterns in biotic crust lichen communities were strongly associated with vegetation, soils, and climate. I hope that my findings will promote intentional management of epiphytic and forest floor cryptogams of western Oregon forests and monitoring of biotic lichen communities in eastern Oregon.
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My thesis explored the effects of and potential mediating mechanisms for an important environmental stressor, ultraviolet-B (UVB) radiation. UVB radiation has negative effects on organisms in both terrestrial ...
Citation Citation
- Title:
- Ultraviolet radiation as an environmental stressor of amphibians
- Author:
- Bancroft, Betsy A.
My thesis explored the effects of and potential mediating mechanisms for an important environmental stressor, ultraviolet-B (UVB) radiation. UVB radiation has negative effects on organisms in both terrestrial and aquatic systems. I used meta-analysis to quantify the effects of UVB radiation on a diversity of aquatic organisms (Chapter 2). UVB negatively affects aquatic organisms by reducing both survival and growth. In particular, UVB reduces growth of embryos more than any other life history stage. Some taxonomic groups may be more affected by UVB radiation than others. In our analysis, the growth of members of the kingdom Protozoa was suppressed by UVB radiation to a greater degree than any other kingdom. These analyses suggest that UVB is an important stressor in both freshwater and marine systems. Amphibians are a common component of freshwater systems and are experiencing world-wide population declines. These declines may be due to a number of causes including habitat loss, introduced species, global climate change, disease, toxic chemicals and UVB radiation. I used meta-analytic techniques to quantify the effects of UVB radiation on amphibians. By synthesizing the results of 41 articles on the effects of UVB radiation on amphibians (Chapter 3), I found a nearly 2-fold reduction in survival of amphibians exposed to UVB radiation. Salamanders (caudates) appear to be more susceptible to damage from UVB than frogs or toads (anurans). Moreover, survival of larvae was much lower than survival of embryos or metamorphic individuals under UVB radiation. In addition, I used factorial meta-analytic techniques to explore the interaction between UVB radiation and other stressors in amphibian habitats. UVB radiation acted synergistically with other stressors to reduce survival of amphibians. Behavioral avoidance of UVB radiation may help mediate the negative effects of UVB radiation on amphibians. In aquatic systems, behavioral avoidance usually requires movement out of shallow water, where UVB levels can be high, into deeper waters with lower UVB transmittance. However, these two microhabitats have very different thermal profiles, creating a trade-off between exploiting warm waters with high UVB levels and avoiding UVB by seeking cooler, deeper regions of ponds. I explored the microhabitat use of larvae of four species through a series of laboratory experiments, field experiments, and observational field transects at three different amphibian habitats (Chapter 4). Larvae did not avoid UVB radiation in either the laboratory or field experiments. Larvae in thermal gradients selected relatively high temperatures regardless of the UVB exposure at these temperatures. In field transects, salamander larvae were most common in deeper, cooler waters where UVB levels were lower. In contrast, anuran larvae were frequently observed in the warmer and shallower regions of each habitat. These regions also had the highest UVB levels, suggesting that anuran larvae are exposed to high levels of UVB due to thermoregulatory behavior. Behavioral avoidance of UVB radiation is not the only mechanism amphibians may use to prevent damage from UVB. Pigments such as melanin may allow larvae to exploit warm shallow waters by absorbing harmful UVB radiation before it causes cellular damage. I tested the efficacy of melanin as a photoprotective pigment in the larvae of two species, Rana cascadae and Pseudacris regilla (Chapter 5). I found no evidence of a photoprotective function for melanin in these larvae. In contrast, lighter colored tadpoles grew more under UVB radiation compared to darker colored tadpoles. Overall, exposure to UVB reduced survival of P. regilla larvae and reduced growth of R. cascadae larvae. Larvae of both of these species were frequently observed in very shallow water with intense solar radiation. This thesis emphasizes the importance of UVB radiation as an environmental stressor in aquatic habitats. Many aquatic organisms are negatively affected by UVB exposure. My thesis work quantitatively demonstrated that UVB radiation is one factor that reduces survival of amphibians and suggests that some species are exposed to high levels of UVB radiation in natural habitats. While UVB radiation is not the sole cause of amphibian population declines, my work suggests that UVB radiation is an important stressor for amphibians that should not be overlooked. In addition, UVB radiation is clearly an important stressor for many other aquatic organisms. Future work should consider the effects of UVB in aquatic systems, particularly the effects of UVB radiation on community structure and ecosystem function.