Introduction


Understanding the impact of unprecedented environmental change on the ecological and evolutionary functionality of ecosystems is a global challenge. Fundamental to addressing this challenge are broad-scale, high-resolution, historical baseline biodiversity data. Although rare, when such datasets are combined with comparable modern data they provide unparalleled insight into the varied ways biodiversity responds to environmental change and the processes governing these responses. A century ago, the American Museum of Natural History (AMNH) conducted a series of pioneering ornithological expeditions in Colombia. Our team, the Colombia Resurvey Project, recently collected modern survey and specimen data from six historical AMNH localities strategically selected to represent the broad spectrum of elevations and land-use dynamics of the tropics.


Objectives



Quantify changes in bird communities and their functional diversity over a century
Quantify changes in the human footprint over a century
Establish the relationship between changes in the human footprint and changes in avian species richness and functional diversity over a century



Methods


We used specimens and bird census data for historical and modern expeditions to document changes in the bird communities a century apart (controlling for sampling bias). We graphed functional diversity space for all six communities in the two time periods, and calculated functional diversity indices (richness, evenness, and divergence).

We compared the human footprint values at different buffers around a site (500m, 1km, 10km, 100km) and used those the values as explanatory variables in a Generalized Linear Mixed Effect Model with species richness and functional diversity indices as response variables.


Results


Changes in avian species richness and functional diversity were context-dependent. Overall, sites had declines in functional diversity but species richness either increased or decreased. Functional groups driving this change were large frugivorous birds (extirpated) and small seed-eating birds (colonizers) in different sites. Sites with significant human footprint increase had more significant decreases in functional diversity. Sites with little change in the human footprint had stable bird community composition and functional diversity. Changes in human footprint were more meaningful at local and landscape scales.


Implications


We show how bird community composition and functional diversity varied over a century of landscape change. The insights gained by comparing these historical and modern biodiversity data are essential to building and improving forecasting models of the impacts of environmental change on biodiversity at multiple temporal scales, preventing extinction, guiding conservation actions, and informing sustainable management.