Amphibian communities and climate change : Where ecological processes meet evolutionary interactions

Forecasts of the impacts of climate change have traditionally focused on individual species and their phenotypes, phenology, or distribution. However, shifts in species distributions and the resulting reorganization of community composition represent an important violation to the assumption of species acting in isolation. Whereas species may respond individualistically to climate change, the manifestations of their responses will be largely influenced by interactions with other organisms. Tractably dealing with complex interaction networks in the face of climate change will require an understanding of community dynamics and the degree to which biotic interactions influence species' behavior, physiology, and survival – and ultimately their footprint on the landscape. To improve our understanding of community-level responses to climate change, I explored amphibian response strategies from both a population- and community-level perspective and provided a critical evaluation of one of the primary methods for incorporating biotic interactions into predictive species distribution models. In Chapter 2, I evaluated amphibian species’ physiological constraints and the potential consequences of phenotypic plasticity as a first step to understanding their sensitivity, and ultimately, adaptive capacity to climate change. I experimentally quantified phenotypic plasticity in larval growth and development in three high elevation Anuran species (Anaxyrus boreas, Pseudacris regilla, and Rana cascadae) in response to projected climate warming scenarios for the Cascade Mountain Range. Warming initiated faster weight gain and accelerated larval growth rates in each of the species. However, any effort to achieve optimum body size (in both length and weight), while maintaining the necessary developmental trajectory under heat stress, was relatively unsuccessful. In Chapter 3, I tested the response strategies of the same three Anuran species to a different climate stressors, hydroperiod reduction (i.e. drought), and included the additional stress of interspecific competition. I found that competition exacerbated the effects of drying on competitively inferior species (Anaxyrus boreas and Pseudacris regilla) and that, in general, species responses were largely context-dependent. My results emphasize the importance of biotic interactions in predictions of species response to climate change. In Chapter 4, I provide a critical evaluation of standard methods for incorporating biotic interactions into predictive species distribution models. Most methods utilize observational data via species co-occurrences on the landscape to infer the role of biotic interactions in structuring species distributions. Results from a series of tests using two long-term amphibian co-occurrence datasets from Mt. Rainier National Park (Washington) and Mt. Hood (Oregon) show that the current best available methods are largely disconnected from community ecology theory and have yet to reconcile the complex dynamics within trophically-structured communities. My research aims to fill a critical knowledge gap in the connection between community dynamics and biogeography, with significant implications for conservation and management of a severely threatened taxonomic group. I highlight the significant challenges of estimating species response to climate change across multiple levels of taxonomic organization and spatio-temporal scales.Keywords: networks, community ecology, climate change, ecology, amphibian, phenotypic plasticit

Evaluating Temporal Consistency in Marine Biodiversity Hotspots

With the ongoing crisis of biodiversity loss and limited resources for conservation, the concept of biodiversity hotspots has been useful in determining conservation priority areas. However, there has been limited research into how temporal variability in biodiversity may influence conservation area prioritization. To address this information gap, we present an approach to evaluate the temporal consistency of biodiversity hotspots in large marine ecosystems. Using a large scale, public monitoring dataset collected over an eight year period off the US Pacific Coast, we developed a methodological approach for avoiding biases associated with hotspot delineation. We aggregated benthic fish species data from research trawls and calculated mean hotspot thresholds for fish species richness and Shannon’s diversity indices over the eight year dataset. We used a spatial frequency distribution method to assign hotspot designations to the grid cells annually. We found no areas containing consistently high biodiversity through the entire study period based on the mean thresholds, and no grid cell was designated as a hotspot for greater than 50% of the time-series. To test if our approach was sensitive to sampling effort and the geographic extent of the survey, we followed a similar routine for the northern region of the survey area. Our finding of low consistency in benthic fish biodiversity hotspots over time was upheld, regardless of biodiversity metric used, whether thresholds were calculated per year or across all years, or the spatial extent for which we calculated thresholds and identified hotspots. Our results suggest that static measures of benthic fish biodiversity off the US West Coast are insufficient for identification of hotspots and that long-term data are required to appropriately identify patterns of high temporal variability in biodiversity for these highly mobile taxa. Given that ecological communities are responding to a changing climate and other environmental perturbations, our work highlights the need for scientists and conservation managers to consider both spatial and temporal dynamics when designating biodiversity hotspots

Patterns and Variation in Benthic Biodiversity in a Large Marine Ecosystem

While there is a persistent inverse relationship between latitude and species diversity across many taxa and ecosystems, deviations from this norm offer an opportunity to understand the conditions that contribute to large-scale diversity patterns. Marine systems, in particular, provide such an opportunity, as marine diversity does not always follow a strict latitudinal gradient, perhaps because several hypothesized drivers of the latitudinal diversity gradient are uncorrelated in marine systems. We used a large scale public monitoring dataset collected over an eight year period to examine benthic marine faunal biodiversity patterns for the continental shelf (55–183 m depth) and slope habitats (184–1280 m depth) off the US West Coast (47°20′N—32°40′N). We specifically asked whether marine biodiversity followed a strict latitudinal gradient, and if these latitudinal patterns varied across depth, in different benthic substrates, and over ecological time scales. Further, we subdivided our study area into three smaller regions to test whether coast-wide patterns of biodiversity held at regional scales, where local oceanographic processes tend to influence community structure and function. Overall, we found complex patterns of biodiversity on both the coast-wide and regional scales that differed by taxonomic group. Importantly, marine biodiversity was not always highest at low latitudes. We found that latitude, depth, substrate, and year were all important descriptors of fish and invertebrate diversity. Invertebrate richness and taxonomic diversity were highest at high latitudes and in deeper waters. Fish richness also increased with latitude, but exhibited a hump-shaped relationship with depth, increasing with depth up to the continental shelf break, ~200 m depth, and then decreasing in deeper waters. We found relationships between fish taxonomic and functional diversity and latitude, depth, substrate, and time at the regional scale, but not at the coast-wide scale, suggesting that coast-wide patterns can obscure important correlates at smaller scales. Our study provides insight into complex diversity patterns of the deep water soft substrate benthic ecosystems off the US West Coast

Warming-induced shifts in amphibian phenology and behavior lead to altered predator-prey dynamics

Climate change induced phenological variation in amphibians can disrupt timesensitive processes such as breeding, hatching, and metamorphosis, and can consequently alter size-dependent interactions such as predation. Temperature can further alter size-dependent, predator-prey relationships through changes in species’ behavior. We thus hypothesized that phenological shifts due to climate warming would alter the predator-prey dynamic in a larval amphibian community through changes in body size and behavior of both the predator and prey. We utilized an amphibian predatorprey system common to the montane wetlands of the U.S. Pacific Northwest: the Long-toed Salamander (Ambystoma macrodactylum) and its anuran prey, the Pacific Chorus Frog (Pseudacris regilla). We conducted predation trials to test if changes in predator phenology and environmental temperature influence predation success. We simulated predator phenological shifts by using different size classes of the long-toed salamander representing an earlier onset of breeding, while using spring temperatures corresponding to early- and mid-season larval rearing conditions. Our results indicated that the predator-prey dynamic was highly dependent upon predator phenology and temperature, and both acted synergistically. Increased size asymmetry resulted in higher tadpole predation rates and tadpole tail damage. Both predators and prey altered activity and locomotor performance in warmer treatments. Consequently, behavioral modifications resulted in decreased survival rates of tadpoles in the presence of large salamander larvae. If predators shift to breed disproportionately earlier than prey due to climate warming, this has the potential to negatively impact tadpole populations in high-elevation amphibian assemblages through changes in predation rates mediated by behavior.Fil: Jara, Fabian Gaston. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Thurman, Lindsey L.. No especifíca;Fil: Montiglio, Pierre Olivier. No especifíca;Fil: Sih, Andrew. No especifíca;Fil: Garcia, Tiffany S.. No especifíca

Number of grid cells (and percentage of total) designated as benthic fish biodiversity hotspots (temporal consistency ranging from 0 years hot to 8 years hot) for Coast-wide and the North biogeographic regions and for the minimum, mean, and maximum universal thresholds and annual threshold calculated for 2003–2010.

<p>Number of grid cells (and percentage of total) designated as benthic fish biodiversity hotspots (temporal consistency ranging from 0 years hot to 8 years hot) for Coast-wide and the North biogeographic regions and for the minimum, mean, and maximum universal thresholds and annual threshold calculated for 2003–2010.</p

North Biogeographic region—location of 1600 km² grid cells with ≥ 3 scientific trawls/year and hotspots for A) benthic fish species richness, and B) benthic fish Shannon diversity, H′.

<p>Each grid cell contains an identification number and shading indicates the number of years (out of 8, 2003–2010) that the cell exceeded the universal threshold value to be classified as a hotspot (31.1 for species richness, 2.37 for Shannon diversity H′).</p

Evaluating Temporal Consistency in Marine Biodiversity Hotspots

<div><p>With the ongoing crisis of biodiversity loss and limited resources for conservation, the concept of biodiversity hotspots has been useful in determining conservation priority areas. However, there has been limited research into how temporal variability in biodiversity may influence conservation area prioritization. To address this information gap, we present an approach to evaluate the temporal consistency of biodiversity hotspots in large marine ecosystems. Using a large scale, public monitoring dataset collected over an eight year period off the US Pacific Coast, we developed a methodological approach for avoiding biases associated with hotspot delineation. We aggregated benthic fish species data from research trawls and calculated mean hotspot thresholds for fish species richness and Shannon’s diversity indices over the eight year dataset. We used a spatial frequency distribution method to assign hotspot designations to the grid cells annually. We found no areas containing consistently high biodiversity through the entire study period based on the mean thresholds, and no grid cell was designated as a hotspot for greater than 50% of the time-series. To test if our approach was sensitive to sampling effort and the geographic extent of the survey, we followed a similar routine for the northern region of the survey area. Our finding of low consistency in benthic fish biodiversity hotspots over time was upheld, regardless of biodiversity metric used, whether thresholds were calculated per year or across all years, or the spatial extent for which we calculated thresholds and identified hotspots. Our results suggest that static measures of benthic fish biodiversity off the US West Coast are insufficient for identification of hotspots and that long-term data are required to appropriately identify patterns of high temporal variability in biodiversity for these highly mobile taxa. Given that ecological communities are responding to a changing climate and other environmental perturbations, our work highlights the need for scientists and conservation managers to consider both spatial and temporal dynamics when designating biodiversity hotspots.</p></div

Location of 1600 km² grid cells with ≥ 3 scientific trawls/year and hotspots for A) benthic fish species richness, and B) benthic fish Shannon diversity, H′.

<p>Each grid cell contains an identification number and shading indicates the number of years (out of 8, 2003–2010) that the cell exceeded the universal threshold value to be classified as a hotspot (34.4 for species richness, 2.42 for Shannon diversity H′).</p

Expanding window approach used to identify cells that contained at least three trawls for each year (2003–2010).

<p>1600 km² (40 x 40 km) cells offered both the highest number of cells that qualified, as well as a high degree of spatial connectivity between the cells.</p

The effect of latitude on model importance for fish and invertebrate richness (S), Shannon diversity (H′) and Rao’s quadratic entropy (Q).

<p>This was determined using the evidence ratio (ρ), which is calculated by first determining the best model using Akaike’s Information Criterion correction (AICc), and then dividing the AICc weight of the model when the term is in the model (w_i) by the AICc weight of the model when the term is removed (w_j). The greater the ρ, the more important latitude is as a predictor in the model.</p><p>The effect of latitude on model importance for fish and invertebrate richness (S), Shannon diversity (H′) and Rao’s quadratic entropy (Q).</p