RESEARCH

#1. PATHWAYS TO ABUNDANCE–OCCUPANCY RELATIONSHIPS: A MECHANISTIC TEST OF THE CORE–SATELLITE, NICHE BREADTH, AND NICHE POSITION HYPOTHESES

seed trap for collecting seed rain from overstory vegetation used as a resource removal trap

A dispersal plot to prevent movement of small mammals into and out of the plot

Abundance–occupancy relationships have been attributed to three non-exclusive processes:

The Core–Satellite Hypothesis (Hanski 1982):
Differences in dispersal ability drive AORs. Widespread “core” species have higher dispersal, facilitating recolonization (rescue effects) and homogenizing population genetic structure, whereas “satellite” species with limited dispersal remain rare and spatially restricted.
The Niche Breadth Hypothesis (Brown 1984):
Generalist species that can use a wide range of food resources are more abundant and widespread than specialists that rely on few or rare foods.
The Niche Position Hypothesis (Hanski et al. 1993):
Common species tend to use resources that are themselves common and widespread, while rare species use resources that are scarce or spatially restricted.

We are testing these hypotheses using long-term small mammal data from the Ungulate Herbivory Under Rainfall Uncertainty (UHURU) experiment at Mpala Conservancy (Laikipia, Kenya).
Our approach combines:

Fecal DNA metabarcoding and vegetation surveys to quantify resource use relative to availability (testing the Niche Breadth and Niche Position hypotheses);
Population genetic analyses (DNA from tail tissue) and dispersal barrier experiments to quantify gene flow and movement patterns (testing the Core–Satellite hypothesis).

Current Collaborators:

Dr. Jacob Goheen (Goheen Research Group) • Dr. Tyler Kartzinel (Kartzinel Lab) •

Dr. Catherine Wagner (Wagner Lab) • Dr. Jessica Rick (Rick Lab)

#2. MECHANISTIC TEST OF THE NICHE VARIATION HYPOTHESIS, OPTIMAL FORAGING THEORY, AND NICHE POSITION HYPOTHESIS IN A SAVANNA SMALL MAMMAL COMMUNITY

While #1 examines AORs at the population level, we also investigate how individual behaviors drive patterns of abundance and resource use. Here, we focus on niche breadth and niche position at the individual level.

Under the Niche Breadth Hypothesis two main hypotheses guide this work:

The Niche Variation Hypothesis (Van Valen 1965): As resources become limiting or population density increases, individuals specialize on subsets of the population’s total diet. Population-level niche breadth expands, but within-individual niche breadth contracts, producing greater differences among individuals.
The Optimal Foraging Theory (MacArthur & Pianka 1966): In contrast, individuals expand their diets as resources change, maintaining broad within-individual niche breadth even as population-level niche breadth increases.

Under the Niche Position Hypothesis:

Niche Position Hypothesis: Predicts that individuals whose diets closely match local resource availability will exhibit higher survival and reproductive success, whereas those with diets deviating from availability will have lower fitness.

We test these predictions using fecal DNA metabarcoding, stable isotope analysis, and mark–recapture data, linking individual dietary strategies to fitness outcomes (survival and reproduction) in small mammals at Mpala Conservancy.

This research reveals how individual-level resource use scales up to population- and species-level ecological patterns, complementing our abundance-occupancy relationship work.

Current Collaborators:

Dr. Jacob Goheen (Goheen Research Group) • Dr. Tyler Kartzinel (Kartzinel Lab)

#3. THE FAST TO SLOW LIFE HISTORY CONTINUUM: DEMOGRAPHY OF THE RUFOUS ELEPHANT SHREW (Elephantulus [Galageska] Rufescens) AND CO-OCCURRING RODENTS

Mammals exhibit a diversity of life history traits falling along a fast-slow continuum. “Fast-living” species exhibit short gestation times, early maturity, and high reproductive rates, whereas the reverse is true for “slow-living” species.

Further, such life history variation should interact with demography, such that slow-living species should be buffered from environmental variability (the demographic buffering hypothesis) and exhibit relatively invariant population growth, while fast-living species should exhibit population growth that tracks environmental variability (the demographic lability hypothesis).

In central Kenya, the rufous elephant shrew (E. rufescens) has a life history toward the “slow” end of the continuum, relative to similarly sized rodents with which it co-occurs. Our research seeks to answer two questions:

How does temporal variation in vital rates and λ (population growth rate) differ between E. rufescens and co-occurring rodents? and
How does the demographic sensitivity of λ to adult survival, adult fecundity, and juvenile survival compare between E. rufescens and co-occurring rodents?

Relevance: As Earth’s climates warm and dry, a major goal at the intersection of life history theory and demography is to predict how species will respond to environmental fluctuations, through the effects of such fluctuations on vital rates and population growth.

Current Collaborators:

Dr. Jacob Goheen (Goheen Research Group) • Prof Daniel Doak (Doak Lab)

#4. LEGACY EFFECTS OF CLIMATE EXTREMES ON EAST AFRICAN SEMI-ARID SAVANNA COMMUNITIES

Extreme climatic events, such as prolonged droughts, can strongly impact ecosystems by altering both plant and animal communities. Understanding which systems resist or recover faster is key to predicting ecosystem stability under climate change.

We are leveraging the extreme drought in Laikipia, Kenya (2020–2023) to study how communities responded across a rainfall gradient, from wetter southern sites to drier northern sites.

Within each site (south, central, and north), we established experimental plots:

Exclosure plots: 1-hectare areas excluding all large mammalian herbivores, replicated three times per site.
Control plots: 1-hectare areas allowing access to all large mammalian ungulates, also replicated three times per site.

This design enables us to evaluate the role of large herbivores in shaping community stability during and after extreme drought. By comparing pre- and post-drought conditions, we track changes in abundance, diversity, and composition across plants and small mammals.

Our main objectives are to assess:

Resistance: How well do communities maintain structure and function during drought?
Resilience: How quickly do communities recover after the drought ends?

By quantifying resistance and resilience along the rainfall gradient and under herbivore exclusion, we aim to identify which systems are most stable and how interactions between herbivory and climate extremes shape savanna ecosystems.

Current Collaborators:

Dr. Jacob Goheen (Goheen Research Group)