As melting ice sheets raised global sea level by more than 100m after the last glacial maximum, hundreds of low-lying basins throughout the Indo-Pacific were inundated forming marine lakes: bodies of seawater entirely surrounded by land. These lakes were inoculated with marine life — from microorganisms to macrobiota — and isolated to varying degrees for the next 6000-15000 years. Understudied and underexplored, marine lakes provide an untapped array of independent evolutionary and ecological experiments into the dimensions of biodiversity, their interactions, and how they may be influenced by environmental change. How did changes in the physical environment influence the relative abundance of living orgamisms within these lakes? Did all lakes undergo the same changes, regardless of their size or proximity to the ocean? These are some of the questions we are examining within this project. This research has been funded by an NSF Dimensions of Biodiversity grant shared between University of California Merced and University of Washington. More to come soon!
Biodiversity is often interpreted as the number of species within a region (species diversity). However, biodiversity comprises additional dimensions, including the evolutionary history (phylogenetic diversity) and the ecological functions (functional diversity) associated with the species in that region. Human activities are driving the loss of species at an unprecedented rate. Yet, we know surprisingly little about how additional dimensions of biodiversity are being impacted by species loss. My research examines the consequences of species loss on the multiple dimensions of biodiversity – primarily functional diversity – in terrestrial tetrapod vertebrates, arguably the most well-studied group of organisms. This is made possible by an integrated dataset of distribution, traits, phylogeny and extinction risk for nearly all terrestrial tetrapod vertebrates of the Western Hemisphere. This research has been funded by an NSF Dimensions of Biodiversity grant shared among NatureServe, IUCN, Temple University's Center for Biodiversity, WSL, University of Wisconsin-Madison, and Auburn University at Mongomery.
Body size is arguably the most important trait of animals, underlying many of their physiological, ecological and evolutionary processes. Therefore, examining the relationship between the body size of animals and their surrounding environment can help us understand why some species are able to occur in certain places but not in others. In the last 12,000 years, humans are known to have had a disproportionate impact on large animals, which are more sensitive to both hunting and land conversion. In this project, we quantified the influence of human pressure history on the distribuion of today's terrestrial vertebrate body sizes across the Western Hemisphere. Overal, we found that areas with a longer history of human pressure include smaller vertebrates than we would expect if humans were absent. However, we also found that not all vertebrate groups have been equally impacted by human pressures, with mammals and birds the most impacted and reptiles and amphibians the least impacted.
Understanding how species' distributions have responded to environmental changes in the past is critical for improving our predictions of the likely future responses of species of management, human and wildlife health and conservation concern. A full understanding of the causes and consequences of species' distribution shifts from empirical data involves two sequential phases: detection and attribution. Detection involves the use of observed distribution data at multiple time periods to identify whether one or multiple species has shifted their geographical distribution. Attribution involves identifying which of a number of hypothesized environmetal drivers underlies the identified shifts in species' distributions. My research has tackled both detection and attribution of species' past distribution shifts with the aim to improve our ability to predict species' future responses to environmental change. This research is in collaboration with University of California Berkeley's Global Change Biology, the UK Biological Records Center and the Natural History Museum of London.
Studies of observed geographic responses to 20th century climate change have principally examined whether observed responses have been consistent with a ubiquitous increase in temperature: a warming fingerprint. In this project, we examined whether recent geographic responses across California in a number of taxonomic groups have been consistent with a warming fingerprint. We found that responses to climate change in the 20th century have been highly heterogeneous and often not consistent with a warming fingerprint. We identified a number of potential direct and indirect mechanisms for these responses, including the influence of aspects of climate change other than temperature (e.g., the shifting seasonal balance of energy and water availability), differences in each taxon’s sensitivity to climate change, trophic interactions, and land-use change.
In a world of rapid environmental change, effective biodiversity conservation and management relies on our ability to detect changes in species occurrence. Ideally, these estimates of change would be derived from long-term monitoring data but such monitoring is costly and rare. An alternative approach is to use historical records from natural history collections as a baseline to compare with recent observations. However, natural history collection data are subject to a number of biases, which have so far prevented their use for estimating temporal changes. In this project, we combined natural history collection data with citizen science observations to identify changes in the occupancy of Californian dragonflies and damselflies over the past century. The approach we used enabled us to correct for a number of the common biases present in natural history collection data. The changes we modeled were consistent with estimates obtained using more standardized survey data. Therefore, our approach enables more robust estimates of temporal trends from natural history collection data, thus facilitating the use of these data in biodiversity conservation and management.
Species distribution models or SDMs are the most commonly used tool to predict species' likely future distribution shifts. Since we are using these models to predict events that are yet to happen, modeled predictions are subject to a high uncertainty. Arguably the best way to assess the ability of these models to predict species' changes over time is to test whether they are able to predict changes that have already happened. In this project, we developed a tool which makes use of increasingly-available data documenting species’ distributions at two time periods to quantify how well species distribution models predict species’ distribution shifts based on given environmental changes.
The emergence rate of new plant diseases is increasing due to novel introductions, climate change, and changes in vector populations, posing risks to agricultural sustainability. Assessing and managing future disease risks depends on understanding the causes of contemporary and historical emergence events. In this project, we examined whether the rise of a disease of potato crops in California at the end of the 20th century has been associated with a population increase in the disease's insect vector. In addition, we also examined if such an expansion may be related to climate change, specifically warmer winters. Using natural history collection data, we found evidence that the insect vector has increased over the last century but these changes appear to be unrelated to climate change.