Download PROJECT SUMMARY: An Integrative Traits

PROJECT SUMMARY: An Integrative Traits-Based Approach to Predicting Variation in Vulnerability of
Tropical and Temperate Stream Biodiversity to Climate Change
Intellectual Merit
Predicting the effect of rapid climate change on biodiversity is an important and urgent scientific challenge. To
date, efforts to predict biodiversity vulnerability have focused on modeling projected temperature increases and
expected latitudinal and elevation range shifts. However, species responses will reflect both the magnitude of
environmental change and their relative sensitivity to that change. We develop a new conceptual framework
that integrates evolutionary and ecological perspectives, unifies disconnected themes of biodiversity theory, and
experimentally quantifies mechanisms of species vulnerability. A consensus is emerging that the historically
more stable thermal conditions of the tropics, where biodiversity is highest, has favored the evolution of narrow
thermal tolerances, reduced dispersal, and smaller geographic ranges of species (Climate Variability
Hypothesis: CVH). As a consequence, tropical species may be more vulnerable than temperate species to a unit
increase in temperature. Another prediction of climate change models is that patterns of precipitation that can
influence patterns of biodiversity through rates of ecosystem disturbance will be modified. We propose to study
biodiversity in tropical and temperate headwater streams, with the overarching goal of predicting how increased
temperature and modified hydrological disturbance regimes interact to shape species vulnerability to climate
change. We will test the hypothesis that species’ physiological vulnerabilities to rapid climate change are
conditional upon historical selection regimes of both temperature and precipitation-driven hydrologic
disturbance across latitude and elevation gradients. Headwater streams are model systems for testing theory
about vulnerability of biodiversity to climate change because: 1) flow dynamics are directly coupled with
precipitation variation, and 2) species performance and abundance as well as ecosystem change can be
efficiently measured and linked to thermal and hydrologic regimes. We will use an integrative, traits-based
approach to quantify species vulnerability in terms of key physiological (thermal tolerance, hypoxia tolerance),
dispersal (gene flow, population genetic structure), and ecological (trophic position) traits that vary across
gradients in temperature (latitude and elevation) and hydrologic disturbance. We focus on small streams in the
Andes of Ecuador (EC) and the Colorado Rockies (CO) that capture alpine-to-piedmont temperature and
precipitation-runoff gradients. Importantly, because oxygen availability declines with elevation, hypoxia
tolerance may be a critical, yet poorly appreciated, functional trait that defines species distribution and
sensitivity to climate warming. Ours will be the first study to fully explore coupled thermal and hypoxia
tolerance and population genetic structure to test the CVH for aquatic insects (EC and CO) and for stream
amphibians (EC). Further, we will conduct experiments in streamside mesocosms and conduct whole stream
diversions and de-oxygenation to quantify how key species under physiological stress of simulated climate
change affect ecosystem processes to understand the higher order consequence of species loss due to modified
thermal or hydrologic regimes. By examining how disturbance-mediated shifts in resource base define the
vulnerability of species to climate change, we will integrate ecosystem context into predictions of species
responses to climate change. Finally, we will extend the generality of our results by testing predictions of the
CVH for a reduced set of stream insects and amphibians for several additional sites that span a broader tropicaltemperate latitudinal gradient. We will use our empirical results on species sensitivities to temperature and
disturbance to generate vulnerability maps using projections of temperature and precipitation change in tropical
and temperate streams.
Broader Impacts
Our extensive species discovery efforts will provide critical, new information on tropical stream insect
diversity, a major faunal group that is poorly studied. The mechanistic framework we propose provides a
general model for how to integrate theory and explicitly link species vulnerability to different components of
climate change, the relative importance of which may vary regionally. We will build extensive international
collaborations and provide training in large-scale collaborative work for numerous postdocs, graduate students,
and undergraduate students in the U.S. and abroad. Our work will provide core science needed to understand
the mechanisms of stream responses to climate change, and thus be of direct relevance to policy makers and
conservation organizations.
Integration
We explicitly integrate taxonomic, functional, and genetic components of biodiversity for two major groups
(insects, amphibians). We also integrate two themes of biodiversity theory (CVH and disturbance) and
components of ecosystem function (stream metabolism and food quality) that can mediate organismal,
population, and species responses to rapid climate change. The conceptual framework we develop and test will
quantify the functional and genetic traits under selection from rapid changes in temperature and O2
concentration, as mediated by hydrologic flow regime (disturbance) and ecosystem context.