Regional variability in landscape effects on forest bird communities

Abstract

Context: Functional responses to landscape heterogeneity are context-dependent, hampering the transferability of landscape-scale conservation initiatives. Japan provides a unique opportunity to test for regional modification of landscape effects due to its broad temperature gradient, coincident with a gradient of historical disturbance intensity. Objectives: To quantify and understand how regional contexts modify forest bird community responses to landscape heterogeneity across Japan. Methods: We characterised the functional trait composition and diversity of breeding bird communities from 297 forest sites, and applied a cross-scale analytical framework to explain regional variation in community responses. Results: The effects of landscape diversity, coincident with forest loss, varied in strength and even direction across the temperature gradient. Cool regions of Japan with highly forested, homogeneous landscapes supported bird communities dominated by forest specialists: those with narrow habitat breadths and insectivorous diets. Warmer regions comprised communities dominated by generalists with wider habitat breadths, even in contiguous, highly forested landscapes. Heterogeneous landscapes selected for generalists, and only promoted functional trait diversity in cool regions where both specialists and generalists can be supplied by a diverse regional pool. Conclusions: Our results provide evidence that regional variation in trait responses to landscape heterogeneity—driven by past environmental filtering and broad-scale climates—leads to differential community responses across Japan. Future research that seeks a nuanced understanding of the regional modification of landscape variables will better serve to inform and target real-world conservation efforts.