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David A. Lytle - One of the best experts on this subject based on the ideXlab platform.
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resistance and resilience of invertebrate communities to seasonal and supraseasonal drought in Arid Land headwater streams
Freshwater Biology, 2015Co-Authors: Michael T. Bogan, Kate S Boersma, David A. LytleAbstract:SUMMARY 1. Climate change is expected to intensify drought in many regions, but ecological impacts on stream communities are poorly understood. Many Arid-Land streams are characterised by predictable seasonal cycles of wetting and drying, to which species are adapted, but unpredictable supraseasonal droughts may constitute extreme events that challenge resident biota. 2. In this article, we synthesise research conducted in Arid-Land streams of the Madrean Sky IsLands (MSI) in Arizona, U.S.A, to evaluate the resistance and resilience of invertebrate communities to drying disturbances caused by normal seasonal drying and severe supraseasonal drought. We also highlight how spatial context (e.g. distance to perennial refuges) influences recovery patterns. 3. Invertebrate community structure changes predictably as habitat contraction progresses from loss of lateral connectivity to complete drying of MSI streams. When drying events are predictable (e.g. seasonal drying), post-drought community recovery is often rapid, since most MSI taxa possess life history traits conferring high resistance and/or resilience to stream drying. 4. Extreme supraseasonal droughts, in contrast, cause unprecedented transitions from perennial to intermittent flow in some MSI streams. While species richness may recover quickly following this flow regime shift, marked turnover in community structure can occur and may delay or preclude recovery to pre-drought conditions. In such cases, short-lived (<1 year) strong dispersers replace relatively long-lived (≥1 year) weak dispersers. As habitat isolation increases, the potential for community recovery from extreme drought decreases. 5. Many MSI aquatic species are threatened by extreme drought. Extinctions of endemic aquatic species due to habitat drying have already been observed in nearby deserts. Further studies are urgently needed to identify drought-sensitive species and understand how the loss of such species may affect stream ecosystem functioning.
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Resistance and resilience of invertebrate communities to seasonal and supraseasonal drought in Arid‐Land headwater streams
Freshwater Biology, 2014Co-Authors: Michael T. Bogan, Kate S Boersma, David A. LytleAbstract:SUMMARY 1. Climate change is expected to intensify drought in many regions, but ecological impacts on stream communities are poorly understood. Many Arid-Land streams are characterised by predictable seasonal cycles of wetting and drying, to which species are adapted, but unpredictable supraseasonal droughts may constitute extreme events that challenge resident biota. 2. In this article, we synthesise research conducted in Arid-Land streams of the Madrean Sky IsLands (MSI) in Arizona, U.S.A, to evaluate the resistance and resilience of invertebrate communities to drying disturbances caused by normal seasonal drying and severe supraseasonal drought. We also highlight how spatial context (e.g. distance to perennial refuges) influences recovery patterns. 3. Invertebrate community structure changes predictably as habitat contraction progresses from loss of lateral connectivity to complete drying of MSI streams. When drying events are predictable (e.g. seasonal drying), post-drought community recovery is often rapid, since most MSI taxa possess life history traits conferring high resistance and/or resilience to stream drying. 4. Extreme supraseasonal droughts, in contrast, cause unprecedented transitions from perennial to intermittent flow in some MSI streams. While species richness may recover quickly following this flow regime shift, marked turnover in community structure can occur and may delay or preclude recovery to pre-drought conditions. In such cases, short-lived (
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invertebrate assemblages of pools in Arid Land streams have high functional redundancy and are resistant to severe drying
Freshwater Biology, 2014Co-Authors: Kate S Boersma, Michael T. Bogan, Brian A. Henrichs, David A. LytleAbstract:Summary Seasonal droughts are predictable components of Arid-Land stream hydrology, and many Arid-Land aquatic taxa have adapted to their extreme environment. However, climate change is altering this predictable hydrology, producing longer and more severe droughts and creating novel disturbance regimes for resident organisms. The hydrologic transitions from flowing stream to fragmented pools to dry stream bed are frequently associated with steep decreases in taxonomic and functional diversity, referred to as thresholds of biodiversity loss. Less is known about how taxa respond between these thresholds, as fragmented pools gradually dry and abiotic conditions intensify. While an increasingly extreme environment may be expected to reduce taxonomic and trait richness, species adapted to predictable seasonal fragmentation may be resistant to declining water levels until all surface water is lost. We used aquatic mesocosms to test two competing hypotheses of the relationship between richness and pool drying for Arid-Land stream invertebrates: (i) the drought vulnerability hypothesis (richness gradually decreases with drying) and (ii) the drought resistance hypothesis (richness remains constant until complete drying occurs). We inoculated replicate mesocosms with aquatic invertebrates from Arid-Land streams in Arizona, U.S.A., and applied three drying treatments representing a continuum of drying stress commonly observed in local streams during the summer dry season (water depths: 10, 7 and 1 cm). Mesocosms were covered to restrict dispersal and colonisation processes and to isolate resistance (in situ survival of species) from resilience (community recovery following disturbance). After 45 days, we destructively sampled all invertebrates in the mesocosms and calculated various taxonomic and functional trait metrics. Taxonomic richness and composition did not differ between drying treatments, providing strong support for the drought resistance hypothesis. Severe drying was associated with lower invertebrate abundances and higher densities than the moderate and control treatments. This finding suggests that density-dependent processes generated by decreased available habitat may be more important determinants of community composition during droughts than abiotic stress in this system. We observed a near-complete overlap of trophic traits (body size and functional feeding group) and resistance traits (respiration mode and diapause) among the three treatments. This high functional redundancy may provide a buffer against changes to ecosystem functioning, even in cases of severe-drying-induced habitat contraction and fragmentation.
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Invertebrate assemblages of pools in Arid‐Land streams have high functional redundancy and are resistant to severe drying
Freshwater Biology, 2013Co-Authors: Kate S Boersma, Michael T. Bogan, Brian A. Henrichs, David A. LytleAbstract:Summary Seasonal droughts are predictable components of Arid-Land stream hydrology, and many Arid-Land aquatic taxa have adapted to their extreme environment. However, climate change is altering this predictable hydrology, producing longer and more severe droughts and creating novel disturbance regimes for resident organisms. The hydrologic transitions from flowing stream to fragmented pools to dry stream bed are frequently associated with steep decreases in taxonomic and functional diversity, referred to as thresholds of biodiversity loss. Less is known about how taxa respond between these thresholds, as fragmented pools gradually dry and abiotic conditions intensify. While an increasingly extreme environment may be expected to reduce taxonomic and trait richness, species adapted to predictable seasonal fragmentation may be resistant to declining water levels until all surface water is lost. We used aquatic mesocosms to test two competing hypotheses of the relationship between richness and pool drying for Arid-Land stream invertebrates: (i) the drought vulnerability hypothesis (richness gradually decreases with drying) and (ii) the drought resistance hypothesis (richness remains constant until complete drying occurs). We inoculated replicate mesocosms with aquatic invertebrates from Arid-Land streams in Arizona, U.S.A., and applied three drying treatments representing a continuum of drying stress commonly observed in local streams during the summer dry season (water depths: 10, 7 and 1 cm). Mesocosms were covered to restrict dispersal and colonisation processes and to isolate resistance (in situ survival of species) from resilience (community recovery following disturbance). After 45 days, we destructively sampled all invertebrates in the mesocosms and calculated various taxonomic and functional trait metrics. Taxonomic richness and composition did not differ between drying treatments, providing strong support for the drought resistance hypothesis. Severe drying was associated with lower invertebrate abundances and higher densities than the moderate and control treatments. This finding suggests that density-dependent processes generated by decreased available habitat may be more important determinants of community composition during droughts than abiotic stress in this system. We observed a near-complete overlap of trophic traits (body size and functional feeding group) and resistance traits (respiration mode and diapause) among the three treatments. This high functional redundancy may provide a buffer against changes to ecosystem functioning, even in cases of severe-drying-induced habitat contraction and fragmentation.
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Flow intermittency alters longitudinal patterns of invertebrate diversity and assemblage composition in an Arid-Land stream network
Freshwater Biology, 2013Co-Authors: Michael T. Bogan, Kate S Boersma, David A. LytleAbstract:SUMMARY 1. Temporary streams comprise a large proportion of the total length of most stream networks, and the great majority of Arid-Land stream networks, so it is important to understand their contribution to biotic diversity at both local and Landscape scales. 2. In late winter 2010, we sampled invertebrate assemblages in 12 reaches of a large Arid-Land stream network (including perennial and intermittent headwaters, intermittent middle reaches and perennial rivers) in south-east Arizona, U.S.A. Intermittent reaches had then been flowing for c. 60 days, following a dry period of more than 450 days. We sampled a subset of the perennial study reaches three more times between 2009 and 2011. Since intermittent reaches were dry during these additional sampling periods, we used assemblage data from two other intermittent streams in the study network (sampled in 2004–05 and 2010) to explore interannual variability in intermittent stream assemblage composition. 3. Invertebrate richness was lowest in intermittent reaches, despite their often being connected to species-rich perennial reaches. The assemblages of these intermittent reaches were not simply a subset of the species in perennial streams, but rather were dominated by a suite of stoneflies, blackflies and midges with adaptations to intermittency (e.g. egg and ⁄ or larval diapause). On average, 86% of individuals in these samples were specialists or exclusive to intermittent streams. Predators were 7–14 times more abundant in perennial than in intermittent reaches. 4. Despite being separated by long distances (12–25 km) and having very different physical characteristics, the assemblages of perennial headwaters and rivers were more similar to one another than to intervening intermittent reaches, emphasising the prime importance of local hydrology in this system. 5. The duration and recurrence intervals of dry periods, and the relative importance of dispersal from perennial refuges, probably influence the magnitude of biological differences between neighbouring perennial and temporary streams. Although perennial headwaters supported the highest diversity of invertebrates, intermittent reaches supported a number of unique or locally rare species and as such contribute to regional species diversity and should be included in conservation planning.
Michael T. Bogan - One of the best experts on this subject based on the ideXlab platform.
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resistance and resilience of invertebrate communities to seasonal and supraseasonal drought in Arid Land headwater streams
Freshwater Biology, 2015Co-Authors: Michael T. Bogan, Kate S Boersma, David A. LytleAbstract:SUMMARY 1. Climate change is expected to intensify drought in many regions, but ecological impacts on stream communities are poorly understood. Many Arid-Land streams are characterised by predictable seasonal cycles of wetting and drying, to which species are adapted, but unpredictable supraseasonal droughts may constitute extreme events that challenge resident biota. 2. In this article, we synthesise research conducted in Arid-Land streams of the Madrean Sky IsLands (MSI) in Arizona, U.S.A, to evaluate the resistance and resilience of invertebrate communities to drying disturbances caused by normal seasonal drying and severe supraseasonal drought. We also highlight how spatial context (e.g. distance to perennial refuges) influences recovery patterns. 3. Invertebrate community structure changes predictably as habitat contraction progresses from loss of lateral connectivity to complete drying of MSI streams. When drying events are predictable (e.g. seasonal drying), post-drought community recovery is often rapid, since most MSI taxa possess life history traits conferring high resistance and/or resilience to stream drying. 4. Extreme supraseasonal droughts, in contrast, cause unprecedented transitions from perennial to intermittent flow in some MSI streams. While species richness may recover quickly following this flow regime shift, marked turnover in community structure can occur and may delay or preclude recovery to pre-drought conditions. In such cases, short-lived (<1 year) strong dispersers replace relatively long-lived (≥1 year) weak dispersers. As habitat isolation increases, the potential for community recovery from extreme drought decreases. 5. Many MSI aquatic species are threatened by extreme drought. Extinctions of endemic aquatic species due to habitat drying have already been observed in nearby deserts. Further studies are urgently needed to identify drought-sensitive species and understand how the loss of such species may affect stream ecosystem functioning.
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Resistance and resilience of invertebrate communities to seasonal and supraseasonal drought in Arid‐Land headwater streams
Freshwater Biology, 2014Co-Authors: Michael T. Bogan, Kate S Boersma, David A. LytleAbstract:SUMMARY 1. Climate change is expected to intensify drought in many regions, but ecological impacts on stream communities are poorly understood. Many Arid-Land streams are characterised by predictable seasonal cycles of wetting and drying, to which species are adapted, but unpredictable supraseasonal droughts may constitute extreme events that challenge resident biota. 2. In this article, we synthesise research conducted in Arid-Land streams of the Madrean Sky IsLands (MSI) in Arizona, U.S.A, to evaluate the resistance and resilience of invertebrate communities to drying disturbances caused by normal seasonal drying and severe supraseasonal drought. We also highlight how spatial context (e.g. distance to perennial refuges) influences recovery patterns. 3. Invertebrate community structure changes predictably as habitat contraction progresses from loss of lateral connectivity to complete drying of MSI streams. When drying events are predictable (e.g. seasonal drying), post-drought community recovery is often rapid, since most MSI taxa possess life history traits conferring high resistance and/or resilience to stream drying. 4. Extreme supraseasonal droughts, in contrast, cause unprecedented transitions from perennial to intermittent flow in some MSI streams. While species richness may recover quickly following this flow regime shift, marked turnover in community structure can occur and may delay or preclude recovery to pre-drought conditions. In such cases, short-lived (
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invertebrate assemblages of pools in Arid Land streams have high functional redundancy and are resistant to severe drying
Freshwater Biology, 2014Co-Authors: Kate S Boersma, Michael T. Bogan, Brian A. Henrichs, David A. LytleAbstract:Summary Seasonal droughts are predictable components of Arid-Land stream hydrology, and many Arid-Land aquatic taxa have adapted to their extreme environment. However, climate change is altering this predictable hydrology, producing longer and more severe droughts and creating novel disturbance regimes for resident organisms. The hydrologic transitions from flowing stream to fragmented pools to dry stream bed are frequently associated with steep decreases in taxonomic and functional diversity, referred to as thresholds of biodiversity loss. Less is known about how taxa respond between these thresholds, as fragmented pools gradually dry and abiotic conditions intensify. While an increasingly extreme environment may be expected to reduce taxonomic and trait richness, species adapted to predictable seasonal fragmentation may be resistant to declining water levels until all surface water is lost. We used aquatic mesocosms to test two competing hypotheses of the relationship between richness and pool drying for Arid-Land stream invertebrates: (i) the drought vulnerability hypothesis (richness gradually decreases with drying) and (ii) the drought resistance hypothesis (richness remains constant until complete drying occurs). We inoculated replicate mesocosms with aquatic invertebrates from Arid-Land streams in Arizona, U.S.A., and applied three drying treatments representing a continuum of drying stress commonly observed in local streams during the summer dry season (water depths: 10, 7 and 1 cm). Mesocosms were covered to restrict dispersal and colonisation processes and to isolate resistance (in situ survival of species) from resilience (community recovery following disturbance). After 45 days, we destructively sampled all invertebrates in the mesocosms and calculated various taxonomic and functional trait metrics. Taxonomic richness and composition did not differ between drying treatments, providing strong support for the drought resistance hypothesis. Severe drying was associated with lower invertebrate abundances and higher densities than the moderate and control treatments. This finding suggests that density-dependent processes generated by decreased available habitat may be more important determinants of community composition during droughts than abiotic stress in this system. We observed a near-complete overlap of trophic traits (body size and functional feeding group) and resistance traits (respiration mode and diapause) among the three treatments. This high functional redundancy may provide a buffer against changes to ecosystem functioning, even in cases of severe-drying-induced habitat contraction and fragmentation.
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Invertebrate assemblages of pools in Arid‐Land streams have high functional redundancy and are resistant to severe drying
Freshwater Biology, 2013Co-Authors: Kate S Boersma, Michael T. Bogan, Brian A. Henrichs, David A. LytleAbstract:Summary Seasonal droughts are predictable components of Arid-Land stream hydrology, and many Arid-Land aquatic taxa have adapted to their extreme environment. However, climate change is altering this predictable hydrology, producing longer and more severe droughts and creating novel disturbance regimes for resident organisms. The hydrologic transitions from flowing stream to fragmented pools to dry stream bed are frequently associated with steep decreases in taxonomic and functional diversity, referred to as thresholds of biodiversity loss. Less is known about how taxa respond between these thresholds, as fragmented pools gradually dry and abiotic conditions intensify. While an increasingly extreme environment may be expected to reduce taxonomic and trait richness, species adapted to predictable seasonal fragmentation may be resistant to declining water levels until all surface water is lost. We used aquatic mesocosms to test two competing hypotheses of the relationship between richness and pool drying for Arid-Land stream invertebrates: (i) the drought vulnerability hypothesis (richness gradually decreases with drying) and (ii) the drought resistance hypothesis (richness remains constant until complete drying occurs). We inoculated replicate mesocosms with aquatic invertebrates from Arid-Land streams in Arizona, U.S.A., and applied three drying treatments representing a continuum of drying stress commonly observed in local streams during the summer dry season (water depths: 10, 7 and 1 cm). Mesocosms were covered to restrict dispersal and colonisation processes and to isolate resistance (in situ survival of species) from resilience (community recovery following disturbance). After 45 days, we destructively sampled all invertebrates in the mesocosms and calculated various taxonomic and functional trait metrics. Taxonomic richness and composition did not differ between drying treatments, providing strong support for the drought resistance hypothesis. Severe drying was associated with lower invertebrate abundances and higher densities than the moderate and control treatments. This finding suggests that density-dependent processes generated by decreased available habitat may be more important determinants of community composition during droughts than abiotic stress in this system. We observed a near-complete overlap of trophic traits (body size and functional feeding group) and resistance traits (respiration mode and diapause) among the three treatments. This high functional redundancy may provide a buffer against changes to ecosystem functioning, even in cases of severe-drying-induced habitat contraction and fragmentation.
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Flow intermittency alters longitudinal patterns of invertebrate diversity and assemblage composition in an Arid-Land stream network
Freshwater Biology, 2013Co-Authors: Michael T. Bogan, Kate S Boersma, David A. LytleAbstract:SUMMARY 1. Temporary streams comprise a large proportion of the total length of most stream networks, and the great majority of Arid-Land stream networks, so it is important to understand their contribution to biotic diversity at both local and Landscape scales. 2. In late winter 2010, we sampled invertebrate assemblages in 12 reaches of a large Arid-Land stream network (including perennial and intermittent headwaters, intermittent middle reaches and perennial rivers) in south-east Arizona, U.S.A. Intermittent reaches had then been flowing for c. 60 days, following a dry period of more than 450 days. We sampled a subset of the perennial study reaches three more times between 2009 and 2011. Since intermittent reaches were dry during these additional sampling periods, we used assemblage data from two other intermittent streams in the study network (sampled in 2004–05 and 2010) to explore interannual variability in intermittent stream assemblage composition. 3. Invertebrate richness was lowest in intermittent reaches, despite their often being connected to species-rich perennial reaches. The assemblages of these intermittent reaches were not simply a subset of the species in perennial streams, but rather were dominated by a suite of stoneflies, blackflies and midges with adaptations to intermittency (e.g. egg and ⁄ or larval diapause). On average, 86% of individuals in these samples were specialists or exclusive to intermittent streams. Predators were 7–14 times more abundant in perennial than in intermittent reaches. 4. Despite being separated by long distances (12–25 km) and having very different physical characteristics, the assemblages of perennial headwaters and rivers were more similar to one another than to intervening intermittent reaches, emphasising the prime importance of local hydrology in this system. 5. The duration and recurrence intervals of dry periods, and the relative importance of dispersal from perennial refuges, probably influence the magnitude of biological differences between neighbouring perennial and temporary streams. Although perennial headwaters supported the highest diversity of invertebrates, intermittent reaches supported a number of unique or locally rare species and as such contribute to regional species diversity and should be included in conservation planning.
Kate S Boersma - One of the best experts on this subject based on the ideXlab platform.
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resistance and resilience of invertebrate communities to seasonal and supraseasonal drought in Arid Land headwater streams
Freshwater Biology, 2015Co-Authors: Michael T. Bogan, Kate S Boersma, David A. LytleAbstract:SUMMARY 1. Climate change is expected to intensify drought in many regions, but ecological impacts on stream communities are poorly understood. Many Arid-Land streams are characterised by predictable seasonal cycles of wetting and drying, to which species are adapted, but unpredictable supraseasonal droughts may constitute extreme events that challenge resident biota. 2. In this article, we synthesise research conducted in Arid-Land streams of the Madrean Sky IsLands (MSI) in Arizona, U.S.A, to evaluate the resistance and resilience of invertebrate communities to drying disturbances caused by normal seasonal drying and severe supraseasonal drought. We also highlight how spatial context (e.g. distance to perennial refuges) influences recovery patterns. 3. Invertebrate community structure changes predictably as habitat contraction progresses from loss of lateral connectivity to complete drying of MSI streams. When drying events are predictable (e.g. seasonal drying), post-drought community recovery is often rapid, since most MSI taxa possess life history traits conferring high resistance and/or resilience to stream drying. 4. Extreme supraseasonal droughts, in contrast, cause unprecedented transitions from perennial to intermittent flow in some MSI streams. While species richness may recover quickly following this flow regime shift, marked turnover in community structure can occur and may delay or preclude recovery to pre-drought conditions. In such cases, short-lived (<1 year) strong dispersers replace relatively long-lived (≥1 year) weak dispersers. As habitat isolation increases, the potential for community recovery from extreme drought decreases. 5. Many MSI aquatic species are threatened by extreme drought. Extinctions of endemic aquatic species due to habitat drying have already been observed in nearby deserts. Further studies are urgently needed to identify drought-sensitive species and understand how the loss of such species may affect stream ecosystem functioning.
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Resistance and resilience of invertebrate communities to seasonal and supraseasonal drought in Arid‐Land headwater streams
Freshwater Biology, 2014Co-Authors: Michael T. Bogan, Kate S Boersma, David A. LytleAbstract:SUMMARY 1. Climate change is expected to intensify drought in many regions, but ecological impacts on stream communities are poorly understood. Many Arid-Land streams are characterised by predictable seasonal cycles of wetting and drying, to which species are adapted, but unpredictable supraseasonal droughts may constitute extreme events that challenge resident biota. 2. In this article, we synthesise research conducted in Arid-Land streams of the Madrean Sky IsLands (MSI) in Arizona, U.S.A, to evaluate the resistance and resilience of invertebrate communities to drying disturbances caused by normal seasonal drying and severe supraseasonal drought. We also highlight how spatial context (e.g. distance to perennial refuges) influences recovery patterns. 3. Invertebrate community structure changes predictably as habitat contraction progresses from loss of lateral connectivity to complete drying of MSI streams. When drying events are predictable (e.g. seasonal drying), post-drought community recovery is often rapid, since most MSI taxa possess life history traits conferring high resistance and/or resilience to stream drying. 4. Extreme supraseasonal droughts, in contrast, cause unprecedented transitions from perennial to intermittent flow in some MSI streams. While species richness may recover quickly following this flow regime shift, marked turnover in community structure can occur and may delay or preclude recovery to pre-drought conditions. In such cases, short-lived (
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invertebrate assemblages of pools in Arid Land streams have high functional redundancy and are resistant to severe drying
Freshwater Biology, 2014Co-Authors: Kate S Boersma, Michael T. Bogan, Brian A. Henrichs, David A. LytleAbstract:Summary Seasonal droughts are predictable components of Arid-Land stream hydrology, and many Arid-Land aquatic taxa have adapted to their extreme environment. However, climate change is altering this predictable hydrology, producing longer and more severe droughts and creating novel disturbance regimes for resident organisms. The hydrologic transitions from flowing stream to fragmented pools to dry stream bed are frequently associated with steep decreases in taxonomic and functional diversity, referred to as thresholds of biodiversity loss. Less is known about how taxa respond between these thresholds, as fragmented pools gradually dry and abiotic conditions intensify. While an increasingly extreme environment may be expected to reduce taxonomic and trait richness, species adapted to predictable seasonal fragmentation may be resistant to declining water levels until all surface water is lost. We used aquatic mesocosms to test two competing hypotheses of the relationship between richness and pool drying for Arid-Land stream invertebrates: (i) the drought vulnerability hypothesis (richness gradually decreases with drying) and (ii) the drought resistance hypothesis (richness remains constant until complete drying occurs). We inoculated replicate mesocosms with aquatic invertebrates from Arid-Land streams in Arizona, U.S.A., and applied three drying treatments representing a continuum of drying stress commonly observed in local streams during the summer dry season (water depths: 10, 7 and 1 cm). Mesocosms were covered to restrict dispersal and colonisation processes and to isolate resistance (in situ survival of species) from resilience (community recovery following disturbance). After 45 days, we destructively sampled all invertebrates in the mesocosms and calculated various taxonomic and functional trait metrics. Taxonomic richness and composition did not differ between drying treatments, providing strong support for the drought resistance hypothesis. Severe drying was associated with lower invertebrate abundances and higher densities than the moderate and control treatments. This finding suggests that density-dependent processes generated by decreased available habitat may be more important determinants of community composition during droughts than abiotic stress in this system. We observed a near-complete overlap of trophic traits (body size and functional feeding group) and resistance traits (respiration mode and diapause) among the three treatments. This high functional redundancy may provide a buffer against changes to ecosystem functioning, even in cases of severe-drying-induced habitat contraction and fragmentation.
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Invertebrate assemblages of pools in Arid‐Land streams have high functional redundancy and are resistant to severe drying
Freshwater Biology, 2013Co-Authors: Kate S Boersma, Michael T. Bogan, Brian A. Henrichs, David A. LytleAbstract:Summary Seasonal droughts are predictable components of Arid-Land stream hydrology, and many Arid-Land aquatic taxa have adapted to their extreme environment. However, climate change is altering this predictable hydrology, producing longer and more severe droughts and creating novel disturbance regimes for resident organisms. The hydrologic transitions from flowing stream to fragmented pools to dry stream bed are frequently associated with steep decreases in taxonomic and functional diversity, referred to as thresholds of biodiversity loss. Less is known about how taxa respond between these thresholds, as fragmented pools gradually dry and abiotic conditions intensify. While an increasingly extreme environment may be expected to reduce taxonomic and trait richness, species adapted to predictable seasonal fragmentation may be resistant to declining water levels until all surface water is lost. We used aquatic mesocosms to test two competing hypotheses of the relationship between richness and pool drying for Arid-Land stream invertebrates: (i) the drought vulnerability hypothesis (richness gradually decreases with drying) and (ii) the drought resistance hypothesis (richness remains constant until complete drying occurs). We inoculated replicate mesocosms with aquatic invertebrates from Arid-Land streams in Arizona, U.S.A., and applied three drying treatments representing a continuum of drying stress commonly observed in local streams during the summer dry season (water depths: 10, 7 and 1 cm). Mesocosms were covered to restrict dispersal and colonisation processes and to isolate resistance (in situ survival of species) from resilience (community recovery following disturbance). After 45 days, we destructively sampled all invertebrates in the mesocosms and calculated various taxonomic and functional trait metrics. Taxonomic richness and composition did not differ between drying treatments, providing strong support for the drought resistance hypothesis. Severe drying was associated with lower invertebrate abundances and higher densities than the moderate and control treatments. This finding suggests that density-dependent processes generated by decreased available habitat may be more important determinants of community composition during droughts than abiotic stress in this system. We observed a near-complete overlap of trophic traits (body size and functional feeding group) and resistance traits (respiration mode and diapause) among the three treatments. This high functional redundancy may provide a buffer against changes to ecosystem functioning, even in cases of severe-drying-induced habitat contraction and fragmentation.
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Flow intermittency alters longitudinal patterns of invertebrate diversity and assemblage composition in an Arid-Land stream network
Freshwater Biology, 2013Co-Authors: Michael T. Bogan, Kate S Boersma, David A. LytleAbstract:SUMMARY 1. Temporary streams comprise a large proportion of the total length of most stream networks, and the great majority of Arid-Land stream networks, so it is important to understand their contribution to biotic diversity at both local and Landscape scales. 2. In late winter 2010, we sampled invertebrate assemblages in 12 reaches of a large Arid-Land stream network (including perennial and intermittent headwaters, intermittent middle reaches and perennial rivers) in south-east Arizona, U.S.A. Intermittent reaches had then been flowing for c. 60 days, following a dry period of more than 450 days. We sampled a subset of the perennial study reaches three more times between 2009 and 2011. Since intermittent reaches were dry during these additional sampling periods, we used assemblage data from two other intermittent streams in the study network (sampled in 2004–05 and 2010) to explore interannual variability in intermittent stream assemblage composition. 3. Invertebrate richness was lowest in intermittent reaches, despite their often being connected to species-rich perennial reaches. The assemblages of these intermittent reaches were not simply a subset of the species in perennial streams, but rather were dominated by a suite of stoneflies, blackflies and midges with adaptations to intermittency (e.g. egg and ⁄ or larval diapause). On average, 86% of individuals in these samples were specialists or exclusive to intermittent streams. Predators were 7–14 times more abundant in perennial than in intermittent reaches. 4. Despite being separated by long distances (12–25 km) and having very different physical characteristics, the assemblages of perennial headwaters and rivers were more similar to one another than to intervening intermittent reaches, emphasising the prime importance of local hydrology in this system. 5. The duration and recurrence intervals of dry periods, and the relative importance of dispersal from perennial refuges, probably influence the magnitude of biological differences between neighbouring perennial and temporary streams. Although perennial headwaters supported the highest diversity of invertebrates, intermittent reaches supported a number of unique or locally rare species and as such contribute to regional species diversity and should be included in conservation planning.
Thomas F. Turner - One of the best experts on this subject based on the ideXlab platform.
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habitat and resource use by larval and juvenile fishes in an Arid Land river rio grande new mexico
Freshwater Biology, 2006Co-Authors: Allison A. Pease, J. Justine Davis, Melanie S. Edwards, Thomas F. TurnerAbstract:SUMMARY 1. Studies of mesic temperate and tropical rivers suggest an important role for floodplain habitats as nursery areas for larval and juvenile fishes. In Arid-Land rivers the extent and duration of flooding is diminished and habitats and resources used by larval fishes are poorly known. Our study documented habitat and resource use of larval fishes in the Rio Grande, New Mexico, an Arid-Land river. 2. Spatial and temporal distribution of larval and juvenile fishes and their inferred microhabitat preferences were studied during spring, summer and autumn, 2003. Stable carbon ( 13 C: 12 C) and nitrogen ( 15 N: 14 N) isotope ratios were measured to identify nutrient sources and characterise trophic positions of young-of-year fishes in this system. 3. Some fishes recruited during high flows (in spring), whereas others recruited during low-flow periods in late summer. Regardless of the timing of reproduction, microhabitats with lower current velocity and higher temperature appeared to serve as vital nursery grounds for Rio Grande fishes. Ephemeral backwaters and disconnected side channels held the highest abundance and diversity of larvae and juveniles. 4. Stable isotope analyses revealed that fish larvae obtained carbon predominately from algal production in early summer, but used organic carbon derived from emergent macrophytes as river discharge decreased in mid-summer. This shift may have been facilitated by microinvertebrate prey that grazed down edible algae and then switched to macrophytes in mid-summer. Nitrogen isotope ratios did not differ among species or early life stages, suggesting that larval and juvenile fishes use similar food resources, especially when restricted to isolated pools in summer.
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Habitat and resource use by larval and juvenile fishes in an Arid‐Land river (Rio Grande, New Mexico)
Freshwater Biology, 2006Co-Authors: Allison A. Pease, J. Justine Davis, Melanie S. Edwards, Thomas F. TurnerAbstract:SUMMARY 1. Studies of mesic temperate and tropical rivers suggest an important role for floodplain habitats as nursery areas for larval and juvenile fishes. In Arid-Land rivers the extent and duration of flooding is diminished and habitats and resources used by larval fishes are poorly known. Our study documented habitat and resource use of larval fishes in the Rio Grande, New Mexico, an Arid-Land river. 2. Spatial and temporal distribution of larval and juvenile fishes and their inferred microhabitat preferences were studied during spring, summer and autumn, 2003. Stable carbon ( 13 C: 12 C) and nitrogen ( 15 N: 14 N) isotope ratios were measured to identify nutrient sources and characterise trophic positions of young-of-year fishes in this system. 3. Some fishes recruited during high flows (in spring), whereas others recruited during low-flow periods in late summer. Regardless of the timing of reproduction, microhabitats with lower current velocity and higher temperature appeared to serve as vital nursery grounds for Rio Grande fishes. Ephemeral backwaters and disconnected side channels held the highest abundance and diversity of larvae and juveniles. 4. Stable isotope analyses revealed that fish larvae obtained carbon predominately from algal production in early summer, but used organic carbon derived from emergent macrophytes as river discharge decreased in mid-summer. This shift may have been facilitated by microinvertebrate prey that grazed down edible algae and then switched to macrophytes in mid-summer. Nitrogen isotope ratios did not differ among species or early life stages, suggesting that larval and juvenile fishes use similar food resources, especially when restricted to isolated pools in summer.
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Genetic and ecological dynamics of species replacement in an Arid-Land river system.
Molecular ecology, 2005Co-Authors: Gregory R. Moyer, Megan J. Osborne, Thomas F. TurnerAbstract:Museum records indicate that Hybognathus placitus was introduced into the Pecos River, New Mexico during the early 1960s. Approximately 10 years later, a congener, Hybognathus amarus, was extirpated from the system. We used microsatellite and mtDNA data, ecological data and modelling, and a computer simulation approach to reconstruct the history of invasion and species replacement. To identify the potential role of hybridization and introgression, we genetically screened H. amarus (n = 389) from the Rio Grande, New Mexico, and H. placitus (n = 424) from the Pecos River, New Mexico using four nuclear microsatellites and a partial fragment of the mtDNA ND4 gene. Assignment tests excluded hybridization as a primary factor in species replacement and suggested a role for interspecific competition. Genetic analyses showed that H. placitus were introduced into the Pecos River from at least two genetically distinct source populations in the Canadian and Red rivers, Oklahoma. Lotka–Volterra models of interspecific competition indicated that the number of founding individuals could have been as few as 20 for H. placitus to have competitively displaced H. amarus in the Pecos River in 10 to 15 generations. Observed differences of allele frequencies between source and founder populations indicated that between 32 and 115 H. placitus individuals founded the Pecos River. Genetic and ecological data suggest that interspecific competition could have led to species replacement in this Arid-Land river system.
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habitat and resource use by larval and juvenile fishes in an Arid Land river rio grande new mexico
Freshwater Biology, 2006Co-Authors: Allison A. Pease, J. Justine Davis, Melanie S. Edwards, Thomas F. TurnerAbstract:SUMMARY 1. Studies of mesic temperate and tropical rivers suggest an important role for floodplain habitats as nursery areas for larval and juvenile fishes. In Arid-Land rivers the extent and duration of flooding is diminished and habitats and resources used by larval fishes are poorly known. Our study documented habitat and resource use of larval fishes in the Rio Grande, New Mexico, an Arid-Land river. 2. Spatial and temporal distribution of larval and juvenile fishes and their inferred microhabitat preferences were studied during spring, summer and autumn, 2003. Stable carbon ( 13 C: 12 C) and nitrogen ( 15 N: 14 N) isotope ratios were measured to identify nutrient sources and characterise trophic positions of young-of-year fishes in this system. 3. Some fishes recruited during high flows (in spring), whereas others recruited during low-flow periods in late summer. Regardless of the timing of reproduction, microhabitats with lower current velocity and higher temperature appeared to serve as vital nursery grounds for Rio Grande fishes. Ephemeral backwaters and disconnected side channels held the highest abundance and diversity of larvae and juveniles. 4. Stable isotope analyses revealed that fish larvae obtained carbon predominately from algal production in early summer, but used organic carbon derived from emergent macrophytes as river discharge decreased in mid-summer. This shift may have been facilitated by microinvertebrate prey that grazed down edible algae and then switched to macrophytes in mid-summer. Nitrogen isotope ratios did not differ among species or early life stages, suggesting that larval and juvenile fishes use similar food resources, especially when restricted to isolated pools in summer.
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Habitat and resource use by larval and juvenile fishes in an Arid‐Land river (Rio Grande, New Mexico)
Freshwater Biology, 2006Co-Authors: Allison A. Pease, J. Justine Davis, Melanie S. Edwards, Thomas F. TurnerAbstract:SUMMARY 1. Studies of mesic temperate and tropical rivers suggest an important role for floodplain habitats as nursery areas for larval and juvenile fishes. In Arid-Land rivers the extent and duration of flooding is diminished and habitats and resources used by larval fishes are poorly known. Our study documented habitat and resource use of larval fishes in the Rio Grande, New Mexico, an Arid-Land river. 2. Spatial and temporal distribution of larval and juvenile fishes and their inferred microhabitat preferences were studied during spring, summer and autumn, 2003. Stable carbon ( 13 C: 12 C) and nitrogen ( 15 N: 14 N) isotope ratios were measured to identify nutrient sources and characterise trophic positions of young-of-year fishes in this system. 3. Some fishes recruited during high flows (in spring), whereas others recruited during low-flow periods in late summer. Regardless of the timing of reproduction, microhabitats with lower current velocity and higher temperature appeared to serve as vital nursery grounds for Rio Grande fishes. Ephemeral backwaters and disconnected side channels held the highest abundance and diversity of larvae and juveniles. 4. Stable isotope analyses revealed that fish larvae obtained carbon predominately from algal production in early summer, but used organic carbon derived from emergent macrophytes as river discharge decreased in mid-summer. This shift may have been facilitated by microinvertebrate prey that grazed down edible algae and then switched to macrophytes in mid-summer. Nitrogen isotope ratios did not differ among species or early life stages, suggesting that larval and juvenile fishes use similar food resources, especially when restricted to isolated pools in summer.