A brief overview of my research program:

My research spans community ecology, biogeography, global change biology and data science. I am driven to understand how ecological and evolutionary processes create and erase biodiversity patterns in plants and animals. I do this by developing and applying computational, modeling and theoretical tools.

I'm most excited by questions that merge local and global scales, and basic and applied research, such as: How can we make community ecology a global science? How can we make macroecology a local science? How can we make global change biology a more predictive science? Answering these questions is crucial to piece together the puzzle of earth's biodiversity, conserve nature as well as humanity, and build a global community of ecologists prepared to tackle the challenges of the 21st century.

My current research program has three main foci; below I outline my past and ongoing work in each area:

  1. Building a global ecology of species interactions

  2. Protecting ecosystems with ecological theory and big data

  3. Untangling biodiversity dynamics across scales

Building a global ecology of species interactions

How many of Earth's flowers were visited by pollinators in the time it took you to read this sentence? How many fruits were eaten, and by which animals? Though we may never answer these questions, we are closer than ever because of ongoing revolutions in big data integration, machine learning, computer vision and remote sensing, to name a few. These revolutions have fueled the expansion of macroecology and biogeography beyond numbers and types of species into the realm of community ecology, which asks how interactions shape assemblage diversity, coexistence and resilience. My goal is to build a global ecology of species interactions to ask the questions of community ecology at the scale of the whole earth.

I am especially interested in trophic interactions, such as those between plants and animals, and the dispersal of seeds in particular. Seed dispersal builds and sustains ecological communities, ecosystems and biomes globally, and seed dispersing animals, perhaps due in part to their often large size, have fascinating patterns of distribution. An overarching goal in this area is to understand how interactions with animals shape the assembly, evolution and spatial structure of plant assemblages, and vice versa.

Relevant papers:
McFadden et al. 2022a. Global plant-frugivore trait matching is shaped by climate and biogeographic history. Ecology Letters, 25:686-696.

Skeels et al. 2023. Paleoenvironments shaped the exchange of terrestrial vertebrates across Wallace’s Line. Science, 381:86-92.

McFadden et al. 2018. Disentangling the functional trait correlates of spatial aggregation in tropical forest trees. Ecology, 100:E02591.

Guevara et al. 2023. Hummingbird community structure and resources modulate the response of interspecific competition to forest conversion. Oecologia, 201:761–770.

Protecting ecosystems with theory and big data

Responses of biodiversity to human impacts, including altered distributions and assemblage turnover patterns, are well-known but difficult to predict. For example, an emerging pattern in global change studies is that terrestrial and aquatic ecosystems can respond in different ways to the same human impact. One potential explanation is that the relative importance of processes governing biodiversity dynamics varies among ecosystems. To help predict idiosyncratic ecosystem responses, I co-developed a framework linking human impacts to ecological processes in terrestrial and freshwater ecosystems. We built on the theory of ecological communities put forth by Mark Vellend that distinguishes four fundamental community processes driving gains and losses of diversity (middle column above).

A major human impact on communities is thermophilization, when assemblage composition shifts towards warm-adapted species. While differences between terrestrial and marine systems in thermophilization rates have been documented, whether these rates differ among terrestrial and freshwater ecosystems is currently unknown. I co-developed an ongoing project to explore this topic through the Blue-Green Biodiversity Initiative. I am also leading a study with the goal of unpacking the land-sea biodiversity paradox, which asks why most of Earth is water but most diversity is found on land. Achieving a more mechanistic understanding of the dynamics of biodiversity in terrestrial and aquatic ecosystems can help us better protect against anthropogenic impacts and aid in their recovery.

Relevant papers:
McFadden et al. 2022b. Linking human impacts to community processes in terrestrial and freshwater ecosystems. Ecology Letters, 26:203-218.

Coelho et al. The geography of climate and the global patterns of species diversity. Nature, 622:537-544.

Jardim de Quieros et al. 2022. Climate, immigration and speciation shape terrestrial and aquatic biodiversity in the European Alps. Proceedings B., 289:20221020.

Cavender-Bares et al. 2018. Ch. 3: Status, trends and future dynamics of biodiversity and ecosystems underpinning nature’s contributions to people. IPBES Regional Assessment for the Americas.

Untangling biodiversity dynamics across scales

What controls diversity? The high diversity of many tropical taxa and decline in diversity away from the Equator has inspired many theories and much debate. The testing of these theories has been hampered historically by a limited ability to separate the effects of multiple processes on diversity patterns. However, recently-developed modeling tools and new datasets are untangling the drivers of diversity dynamics. I am particularly interested in parsing abiotic effects from those of dispersal limitation, biogeographic history and species interactions. Below I outline my research on this topic from local to global scales.

At the local scale in the Amazon (left panel above), I collected a newly-developed drought tolerance trait for >100 tree species, and found it was predictive of species associations with drier ridge-tops versus wetter valleys. However, spatial point process modeling of >450 tree species revealed that dispersal limitation was also an important driver of stem clustering, which is linked to the mass of tree’s seeds.

At the regional scale for the Americas (middle panel), I found that temperature was the best predictor of taxonomic and phylogenetic community turnover, aka beta diversity, for >81,000 species of vascular plants. This suggests that ongoing climate change will cause shifts in diversity regionally and perhaps globally. A major result of this study was a ‘reverse’ latitudinal gradient in which, contrary to expectations, the largest deep-time separations among neighboring assemblages occurred outside of the tropics.

However, the two beta diversity metrics we used were not directly comparable. To overcome this limitation, I co-developed a method to partition a single community turnover metric into more recent and deep-time components, and used the method to map global hotspots of both recent and ancestral components of turnover for 8,296 bird species (right panel). The results of these studies suggest that the multiple processes that combine and interact to create diversity patterns can be untangled with appropriate tools and datasets.

Relevant papers:
McFadden et al. 2019. Temperature shapes opposing latitudinal gradients of plant taxonomic and phylogenetic β diversity. Ecology Letters, 22:1126-1135.

McFadden et al. 2022a. Global plant-frugivore trait matching is shaped by climate and biogeographic history. Ecology Letters, 25:686-696.

Skeels et al. 2023. Paleoenvironments shaped the exchange of terrestrial vertebrates across Wallace’s Line. Science, 381:86-92.

Coelho et al. The geography of climate and the global patterns of species diversity. Nature, 622:537-544.

McFadden et al. 2018. Disentangling the functional trait correlates of spatial aggregation in tropical forest trees. Ecology, 100:E02591.

McFadden et al. 2020. Global hotspots of recent and ancestral turnover in birds. Research Square Preprint.

A big thank you to the funders of my current and past research: