The Biogeography of Ecosystem Flows

A study by Bhavya Palugudi (MSc, Ecosystems Lab)

Bhavya Palugudi, an MSc student in the Ecosystems Lab, has been exploring how energy flows can be used to understand biogeographic differences in animal‑mediated ecosystem functioning across tropical forests. Tropical systems vary widely in structure, composition, and ecological dynamics, and these differences are shaped by long‑term biogeographic processes. By quantifying energy consumption across animal guilds, Bhavya examined how fine‑scale variation in energy pathways emerges in different forest communities.

Her study compared three old‑growth forest sites in Borneo with the Cocha Cashu Biological Station in Manu National Park, Peru. Despite the absence of megaherbivores since the late Pleistocene, Peruvian mammals showed higher overall consumption than those in Borneo. In contrast, passerine birds accounted for a larger share of consumption in Borneo, whereas Peruvian bird communities displayed a more even distribution of energy use. Both systems showed clear size‑structured partitioning of energy pathways, raising questions about the consequences of size‑selective species loss in the future.

A Borneo forest. Photo credit: Francisco Navarro Rosales

Across sites, certain guild‑level patterns were consistent. Invertivores dominated energy flow in both forests, terrestrial omnivores played a larger functional role in Peru, and terrestrial herbivores were major contributors in both regions. Canopy herbivory was more prominent in Peru, likely due to the higher availability of edible canopy foliage.

Bhavya also used the Energetic Shannon–Wiener Index (ESWI) to assess the diversity of energy pathways. Surprisingly, most guilds showed similar energetic distributions across the two tropical systems despite large differences in species richness. This suggests a potential threshold beyond which additional species do not increase the diversity of energy flows. When compared to temperate and polar systems such as Wytham Woods and Greenland, ESWI values declined sharply, regardless of whether bird or mammal energy flows were considered. Notably, Borneo exhibited lower species richness but higher ESWI, while Peru showed the opposite pattern, challenging assumptions embedded in the diversity–stability hypothesis.

Wytham Woods (left; photo credit: Cecilia Dahlsjö) and Greenland (right; photo credit: Monica Groth) as comparative ecosystems to the tropical systems investigated in this study.

The implications for ecosystem assessment are significant. High species richness is often assumed to indicate high functional integrity, yet Bhavya’s results show that Borneo has higher energy flow despite Peru’s greater species richness. In Wytham Woods, extremely high mammal energy flow is driven largely by invasive deer and potentially amplified by predator absence, raising questions about how energetics should inform definitions of ecosystem “health.”

Future work will involve constructing food‑web networks for Wytham Woods to quantify trophic interaction strengths and their influence on energy fluxes. Expanding this approach across additional biogeographic realms and ecosystem types will help determine whether the observed patterns represent general principles of ecosystem energetics.

We will link Bhavya's paper here when it becomes available online.