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Neighborhood watch: Why closely related tropical animals live together

A cross-institutional team of researchers from Macquarie University, UNSW and the University of Nebraska has unpicked the reasons why hundreds of bat and bird species across Central and South America live in close proximity. The answer lies in their family trees.

A new study in the Proceedings of the Royal Society B: Biological Sciences has analyzed 190 bat species and 1,197 bird species across 95 locations from Mexico to Argentina.

Using advanced computer modeling, the research team examined three factors influencing where species live together: family relationships, diet and human impact.

"We found that closely related species are much more likely to live together than distant relatives," says Associate Professor John Alroy, a paleobiologist from Macquarie University's School of Natural Sciences. "Possibly, the shared evolutionary history of related species means they also share similar needs, allowing them to coexist in the same places."

Previous studies had looked at species pairs individually, which made it hard to detect clear patterns. The team's new method gave a broader overview.

Lead author Dr. Anikó Tóth, a conservation scientist from UNSW, says the findings challenge ideas about competition driving species apart: "Rather than competing species avoiding each other, we found that animals with similar needs, especially close relatives, tend to group together in suitable habitats."

Species that eat similar foods showed more varied patterns in where they lived than those with different diets, suggesting food competition can lead to different outcomes—sometimes species avoid each other; sometimes they share resources.

For bats, the research found an unexpected pattern where species with somewhat similar diets were more likely to live together than those with either very similar or very different diets.

"We think having slightly different needs can help species coexist because it reduces direct competition, while they can still both benefit from shared habitat preferences," says Dr. Tóth.

Senior author Associate Professor Andrew Allen, a theoretical biologist at Macquarie University, worked with Dr. Tóth to develop a new class of statistical models that allows the effects of multiple factors on cohabitation to be teased apart.

"This method represents a major advance in studying biodiversity patterns across large areas," says Associate Professor Allen. "It could also be used to address questions in many other fields, including genomics and the social sciences."

The research has important implications for understanding how animal communities form and how they might respond to environmental change. The findings suggest evolutionary history creates predictable patterns in how species spread across landscapes.

The study represents one of the largest analyses of its kind in the highly biodiverse Neotropical region. The researchers used data from 90 bat studies and 71 bird studies.