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Current Research

Humans are transforming faunal communities at scales both global and local through biodiversity loss and species invasion. We are increasingly aware that these faunal changes are not merely a conspicuous consequence of human impacts on the planet, but are also primary drivers of global change in their own right.  Faunal loss or addition can have cascading effects on global scale patterns of nutrient movement, continental climate regimes, energy flow both within and across ecosystems, and human health and well-being. However, our efforts to fully understand and predict, much less prevent, such ecological disassembly and functional loss has been deeply hindered by the complex and context dependent nature of community responses to biotic disturbance.  For example there is strong evidence for synergies between faunal loss and climate change, in part because climate systematically mediates the ways in which wildlife interact with and modify their habitat, however such synergies and feedback loops are not yet incorporated into either conservation or climate projections.

Although identifying and understanding the synergistic effects of biodiversity loss and other aspects of global change on ecosystem stability and function has repeatedly been identified as a research and conservation priority, we still have much work ahead of us in order to address this challenge. Much of the research in our lab is thus dedicated to understanding the extent to which changing environmental context (as caused, for instance, by climate change and habitat fragmentation) affects stability of ecosystems and their functions following biodiversity loss. While we look at a range of functional responses to biodiversity change, I am particularly interested in effects for disease prevalence and health of both humans and wildlife in natural and disturbed ecosystems.  

Below we highlight a few of the projects currently active in the lab.

 

The role of watering holes in concentrating parasites in a changing climate (Funding through NSF DEB 1556786)

Fig 1. Zebra visiting a watering hole in Kenya.
Watering holes in the East African tropical savanna are hubs of animal life, from the smallest insects to the large megafauna that captivate human attention. In the midst of changing climate, animal habitat loss, and increasing human water demands, these iconic resource sites are likely to experience similar drastic changes in their volume, water quality, and relationship with animals and humans. One considerably important feature of watering holes is their potential role in concentrating parasites, as watering holes are some of the most highly-trafficked sites by a full range of tropical savanna wildlife. These water points could provide increased transmission potential among and within species, in addition to increased parasite survivorship or reproduction at higher humidity. Temperature and rainfall clearly affect individual watering hole properties, but these climate factors can also influence immunosuppression of hosts under stress, and range expansions and shifts of hosts and parasites due to changing thermal limits. In light of this, our study, led by PI Hillary Young and PhD student Georgia Titcomb, focuses on two core objectives: 1) to quantify the effect of watering holes on richness and density of parasites using both observational and experimental approaches across climate gradients; and 2) to isolate the effects of changes in climate and wildlife abundance on parasite density in and around watering holes.

 

The role of large wildlife on carbon flux and storage on an ecosystem scale (Funding through NGS Young Explorer Grant)

Fig 2. Transect line within the Kenya Long-term Exclosure Experiment (KLEE).
Traditionally, carbon flux and storage estimates do not incorporate the effects that large-bodied organisms have on carbon in, and released from, an ecosystem; to that end, PhD student Elizabeth Forbes is interested in illuminating the direct and indirect effects of the loss of these organisms  on carbon as it pertains to its storage and release to the atmosphere.  This is increasingly relevant as the planet experiences changes characteristic of the Anthropocene, like climate change and biodiversity loss, that may have interacting effects on carbon.  Most recently, Elizabeth has been exploring this question in a Kenyan savanna, where she is working on field experiments aiming to quantify the differences in soil respiration, leaf litter decomposition, and invertebrate biomass in experimental plots where large, charismatic fauna have been excluded for 20 years.

 

 

Using replicated empirical networks to understand drivers of ecosytem structure and stability (Funding through NSF DEB-1457371)

Fig 3. The atoll of Palmyra (A) is an ideal location to ask questions about the abiotic drivers of foodweb structure. It consists of 23 islets ranging from 0.05 ha (B) to over 250 ha. The islets have relatively simple food chains with various species of geckos (C), and spiders as top predators. Islets span a 10 fold gradient in productivity that is driven by variation in seabird density and associated nutrient inputs (D).

Ecosystems and communities are made up of complex interactions of species and their abiotic environments. Consequently, perturbations such as species loss or invasion likely have many and unpredictable cascading effects across complex interacting systems. In a time when humans are continuing to fragment and change the abiotic characteristics of environments as well as add and remove species at alarming rates, it becomes imperative to understand and predict how dynamic webs of interactions will respond.

 We chose to shed light on this challenge by 1.) constructing highly-resolved empirical food webs for Palmyra Atoll, and 2.) using these empirical webs to inform dynamic food web models. Palmyra Atoll is a low-lying coral atoll consisting of ~25 smaller islets that range independently in size and productivity. In 2011, rats were eradicated from the atoll. The abiotic environmental gradient  along with the rat eradication enables us to construct replicated webs from different abiotic environments both before and after a species loss. This suite of replicated webs allows us to see how environmental factors drive food web structure, and how dynamic webs respond after losing a dominant consumer. Our research team includes PI’s Hillary Young and Kevin Lafferty, postdoctoral fellow John McLaughlin, and PhD student Ana Miller-ter Kuile. 

 

The influence of climate change and mammal community change on zoonotic disease in California (Funding through the Hellman Foundation, the Worster Family Foundation, and UC Santa Barbara)

Fig 4. Wildflowers growing within the study site.

Large wildlife are declining at both local and global scales, creating cascading effects across virtually every ecosystem on Earth. However, our efforts to fully understand the consequences of these extirpations and extinctions have been deeply hindered by the highly variable and complex nature of community responses. In particular, synergies among wildlife loss and climate change can amplify impacts on ecosystem structure, function, and provisioning of environmental services to humans.

Large wildlife are common in many places where temperature and precipitation are likely to shift dramatically, such as California, where model-averaged climate projections predict temperature increases of 2-4°C and more frequent and severe droughts over the next century. Because large animals are exceptionally vulnerable to anthropogenic influences (including climate change, land use shifts, and pastoralism), understanding their roles in structuring dynamic ecosystems is critical as we move forward in a rapidly changing world.

Fig 5. Elk captured with a wildlife camera.

 

We have recently begun a project in the mountains of south-central California to explore the interactive effects of climate change and large mammal loss on a critical ecosystem function: control of vector-borne disease. Ticks are among the top zoonotic disease vectors in the world, carrying a diverse suite of pathogens relevant to the humans, domestic animals, and wildlife. In California, these include the causative agents of Lyme disease, Anaplasmosis, Tularemia, and Babesia. Large mammals can affect ticks through direct and indirect mechanisms: although they can increase tick abundance by providing blood meals for adults, they may also decrease abundance by reducing habitat value for ticks and small vertebrate hosts via herbivory, predation, trampling or soil compaction.

We are using a series of 27 1-ha experimental plots that manipulate large mammal abundance across a steep climate gradient. Led by PI Hillary Young and PhD student Devyn Orr, our study seeks to answer two primarily questions: 1) Does large wildlife removal impact abundance of ticks and tick borne disease; and 2) does climate moderate large wildlife removal effects?