Search

Search Results

• 1. [Article] Fish Species Introductions Provide Novel Insights into the Patterns and Drivers of Phylogenetic Structure in Freshwaters

  Despite long-standing interest of terrestrial ecologists, freshwater ecosystems are a fertile, yet unappreciated, testing ground for applying community phylogenetics to uncover mechanisms of species assembly. ...

  Citation × Citation Citation Abstract Copy Title: Fish Species Introductions Provide Novel Insights into the Patterns and Drivers of Phylogenetic Structure in Freshwaters Author: Strecker, Angela L., Olden, Julian D. Year: 2014 Despite long-standing interest of terrestrial ecologists, freshwater ecosystems are a fertile, yet unappreciated, testing ground for applying community phylogenetics to uncover mechanisms of species assembly. We quantify phylogenetic clustering and overdispersion of native and non-native fishes of a large river basin in the American Southwest to test for the mechanisms (environmental filtering versus competitive exclusion) and spatial scales influencing community structure. Contrary to expectations, non-native species were phylogenetically clustered and related to natural environmental conditions, whereas native species were not phylogenetically structured, likely reflecting human-related changes to the basin. The species that are most invasive (in terms of ecological impacts) tended to be the most phylogenetically divergent from natives across watersheds, but not within watersheds, supporting the hypothesis that Darwin's naturalization conundrum is driven by the spatial scale. Phylogenetic distinctiveness may facilitate non-native establishment at regional scales, but environmental filtering restricts local membership to closely related species with physiological tolerances for current environments. By contrast, native species may have been phylogenetically clustered in historical times, but species loss from contemporary populations by anthropogenic activities has likely shaped the phylogenetic signal. Our study implies that fundamental mechanisms of community assembly have changed, with fundamental consequences for the biogeography of both native and non-native species. Title: Fish Species Introductions Provide Novel Insights into the Patterns and Drivers of Phylogenetic Structure in Freshwaters Author: Strecker, Angela L., Olden, Julian D. Year: 2014 Despite long-standing interest of terrestrial ecologists, freshwater ecosystems are a fertile, yet unappreciated, testing ground for applying community phylogenetics to uncover mechanisms of species assembly. We quantify phylogenetic clustering and overdispersion of native and non-native fishes of a large river basin in the American Southwest to test for the mechanisms (environmental filtering versus competitive exclusion) and spatial scales influencing community structure. Contrary to expectations, non-native species were phylogenetically clustered and related to natural environmental conditions, whereas native species were not phylogenetically structured, likely reflecting human-related changes to the basin. The species that are most invasive (in terms of ecological impacts) tended to be the most phylogenetically divergent from natives across watersheds, but not within watersheds, supporting the hypothesis that Darwin's naturalization conundrum is driven by the spatial scale. Phylogenetic distinctiveness may facilitate non-native establishment at regional scales, but environmental filtering restricts local membership to closely related species with physiological tolerances for current environments. By contrast, native species may have been phylogenetically clustered in historical times, but species loss from contemporary populations by anthropogenic activities has likely shaped the phylogenetic signal. Our study implies that fundamental mechanisms of community assembly have changed, with fundamental consequences for the biogeography of both native and non-native species. Close

• 2. [Article] OSMB AIS Funds Final Report: Task 1 Boat Ramp Monitoring for New Zealand Mud Snails

  The New Zealand mud snail (Potamopyrgus antipodarum; NZMS) is an invasive species found in a variety of ecosystems in Oregon, including brackish estuaries, heavily used recreational rivers, and highly ...

  Citation × Citation Citation Abstract Copy Title: OSMB AIS Funds Final Report: Task 1 Boat Ramp Monitoring for New Zealand Mud Snails Author: Brenneis, Valance, Cimino, Samuel, Strecker, Angela L. Year: 2013 The New Zealand mud snail (Potamopyrgus antipodarum; NZMS) is an invasive species found in a variety of ecosystems in Oregon, including brackish estuaries, heavily used recreational rivers, and highly trafficked coastal freshwater lakes. NZMS are an invasive species of concern because once established, they may out-compete native invertebrate grazers, such as native insect larvae that provide important food resources for fish, and NZMS themselves provide little nutritional value. Monitoring for the presence and population density of NZMS was performed at boat ramps located along several water bodies in 2006 – 2007. These water bodies were then re-sampled during the summer of 2012 and winter of 2013 to investigate changes in population densities, as well as the potential spread of NZMS. In addition, six brackish estuaries and six freshwater coastal lakes were sampled in the summer of 2013 once again for population densities but also for stable isotope analysis to better understand the influence NZMS may have on these different ecosystem food webs. This work addresses how NZMS densities differ across invaded sites, how densities vary over time, how community diversity in rivers and estuaries varies between sites and over time, whether there is a correlation between NZMS densities and invertebrate diversity, and whether NZMS density correlates with decreasing dietary specificity for competing benthic invertebrates. Samples were sorted, identified, and counted, and stable isotope analyses from the summer 2013 field season were conducted on macroinvertebrates, zooplankton, and primary producers at the UC Davis Stable Isotope Facility. NZMS densities were found to be dynamic, with population densities increasing and decreasing over time and space. Additionally, two waterbodies (the lower Siuslaw River and the Nestucca River Estuary) previously without reported NZMS presence were identified to have established NZMS populations. Across invaded sites during the 2006 and 2012 sampling periods, there was a strong negative correlation between NZMS density and the diversity of the benthic invertebrate community. Within sites, no significant correlation was detected. High NZMS population densities were found to have a significantly negative relationship with detritivore density populations in the freshwater lake sites sampled in the summer of 2013. There were no significant relationships between NZMS and the density of any particular macroinvertebrate feeding habit group in estuaries. Additionally, stable isotope analyses indicated that NZMS at high population densities in the freshwater lakes share a similar stable isotope signature with macroinvertebrate herbivores, but NZMS had a more specific or narrow dietary range suggesting macroinvertebrate herbivores had more generalized diets than NZMS when at high densities. Conversely, NZMS population densities in the brackish estuary ecosystems showed no discernable patterns from the stable isotope analyses to indicate that their presence, either at high or low density, had an effect on the estuarine food webs. We concluded that continued research on long term population dynamics of invasive species like NZMS and their effects on native food webs remain crucial to future management and mitigation. Title: OSMB AIS Funds Final Report: Task 1 Boat Ramp Monitoring for New Zealand Mud Snails Author: Brenneis, Valance, Cimino, Samuel, Strecker, Angela L. Year: 2013 The New Zealand mud snail (Potamopyrgus antipodarum; NZMS) is an invasive species found in a variety of ecosystems in Oregon, including brackish estuaries, heavily used recreational rivers, and highly trafficked coastal freshwater lakes. NZMS are an invasive species of concern because once established, they may out-compete native invertebrate grazers, such as native insect larvae that provide important food resources for fish, and NZMS themselves provide little nutritional value. Monitoring for the presence and population density of NZMS was performed at boat ramps located along several water bodies in 2006 – 2007. These water bodies were then re-sampled during the summer of 2012 and winter of 2013 to investigate changes in population densities, as well as the potential spread of NZMS. In addition, six brackish estuaries and six freshwater coastal lakes were sampled in the summer of 2013 once again for population densities but also for stable isotope analysis to better understand the influence NZMS may have on these different ecosystem food webs. This work addresses how NZMS densities differ across invaded sites, how densities vary over time, how community diversity in rivers and estuaries varies between sites and over time, whether there is a correlation between NZMS densities and invertebrate diversity, and whether NZMS density correlates with decreasing dietary specificity for competing benthic invertebrates. Samples were sorted, identified, and counted, and stable isotope analyses from the summer 2013 field season were conducted on macroinvertebrates, zooplankton, and primary producers at the UC Davis Stable Isotope Facility. NZMS densities were found to be dynamic, with population densities increasing and decreasing over time and space. Additionally, two waterbodies (the lower Siuslaw River and the Nestucca River Estuary) previously without reported NZMS presence were identified to have established NZMS populations. Across invaded sites during the 2006 and 2012 sampling periods, there was a strong negative correlation between NZMS density and the diversity of the benthic invertebrate community. Within sites, no significant correlation was detected. High NZMS population densities were found to have a significantly negative relationship with detritivore density populations in the freshwater lake sites sampled in the summer of 2013. There were no significant relationships between NZMS and the density of any particular macroinvertebrate feeding habit group in estuaries. Additionally, stable isotope analyses indicated that NZMS at high population densities in the freshwater lakes share a similar stable isotope signature with macroinvertebrate herbivores, but NZMS had a more specific or narrow dietary range suggesting macroinvertebrate herbivores had more generalized diets than NZMS when at high densities. Conversely, NZMS population densities in the brackish estuary ecosystems showed no discernable patterns from the stable isotope analyses to indicate that their presence, either at high or low density, had an effect on the estuarine food webs. We concluded that continued research on long term population dynamics of invasive species like NZMS and their effects on native food webs remain crucial to future management and mitigation. Close

• 3. [Article] Direct and Indirect Effects of an Invasive Planktonic Predator on Pelagic Food Webs

  The relative importance of top-down invader effects relative to environmental drivers was determined by sampling crustacean zooplankton, rotifer, and phytoplankton communities in a set of invaded and noninvaded ...

  Citation × Citation Citation Abstract Copy Title: Direct and Indirect Effects of an Invasive Planktonic Predator on Pelagic Food Webs Author: Strecker, Angela L., Beisner, Beatrix E., Arnott, Shelley E., Paterson, Andrew M., Winter, Jennifer G., Johannsson, Ora E., Yan, Norman D. Year: 2011 The relative importance of top-down invader effects relative to environmental drivers was determined by sampling crustacean zooplankton, rotifer, and phytoplankton communities in a set of invaded and noninvaded reference lakes. The non-native invertebrate predator Bythotrephes had significant effects on zooplankton community size structure, rotifers, and phytoplankton taxonomic composition, but no significant effects on crustacean zooplankton taxonomic and functional group composition. Part of the variation in phytoplankton communities was explained by the presence of the invader. Because Bythotrephes is generally known to be a carnivore and to not consume phytoplankton, this effect is likely mediated by the zooplankton community’s response to environmental gradients. Although Bythotrephes appears to indirectly alter phytoplankton composition in invaded lakes, there was no evidence of a trophic cascade, and edible phytoplankton biovolume did not increase in invaded lakes. These complex direct and indirect interactions suggest that effects of invaders may be highly context-dependent, and therefore pose a significant challenge for predicting wider community and ecosystem responses. Title: Direct and Indirect Effects of an Invasive Planktonic Predator on Pelagic Food Webs Author: Strecker, Angela L., Beisner, Beatrix E., Arnott, Shelley E., Paterson, Andrew M., Winter, Jennifer G., Johannsson, Ora E., Yan, Norman D. Year: 2011 The relative importance of top-down invader effects relative to environmental drivers was determined by sampling crustacean zooplankton, rotifer, and phytoplankton communities in a set of invaded and noninvaded reference lakes. The non-native invertebrate predator Bythotrephes had significant effects on zooplankton community size structure, rotifers, and phytoplankton taxonomic composition, but no significant effects on crustacean zooplankton taxonomic and functional group composition. Part of the variation in phytoplankton communities was explained by the presence of the invader. Because Bythotrephes is generally known to be a carnivore and to not consume phytoplankton, this effect is likely mediated by the zooplankton community’s response to environmental gradients. Although Bythotrephes appears to indirectly alter phytoplankton composition in invaded lakes, there was no evidence of a trophic cascade, and edible phytoplankton biovolume did not increase in invaded lakes. These complex direct and indirect interactions suggest that effects of invaders may be highly context-dependent, and therefore pose a significant challenge for predicting wider community and ecosystem responses. Close