Interactive effects of fire and habitat loss shape dietary trait structure of bird communities in tropical forests

Overview

This study examines the interactive effects of fire and habitat loss on the functional trait structure of bird communities in Atlantic Forest landscapes of southeastern Brazil. Using point count surveys across 15 landscapes with paired burned and unburned sites, the research quantifies community-weighted means and variances of continuous dietary traits to assess how fire severity, fire extent, and forest cover jointly shape dietary trait composition. The analysis reveals non-additive and synergistic interactions between fire disturbance and habitat loss in driving changes to community trait structure.

Methods and approach

Bird surveys were conducted using point count methods across 30 sampling units distributed across 15 Atlantic Forest landscapes, with paired burned and unburned forest sites in each landscape. Community trait structure was quantified using community-weighted means and community-weighted variances derived from continuous dietary traits representing proportional use of different food resources. Trait estimates were generated through nonparametric bootstrapping approaches. Generalized linear mixed models were employed to assess the independent and interactive effects of fire disturbance metrics (severity and extent) and forest cover on trait metrics, with landscape included as a random effect to account for spatial structure.

Key Findings

Fire disturbance influenced both community-weighted means and variances of dietary traits, with responses strongly modulated by forest cover levels. High fire disturbance combined with low forest cover resulted in trait convergence, manifested as reduced variability in fruit, nectar, and invertebrate consumption, indicating strong environmental filtering of the community. Conversely, burned forests exhibited increased variance in seed consumption, suggesting trait divergence consistent with limiting similarity mechanisms operating under enhanced post-fire resource heterogeneity. These patterns demonstrate that environmental filtering and limiting similarity processes can operate simultaneously along disturbance gradients, their relative importance depending on both trait identity and landscape context.

Implications

The findings establish that trait-based analytical approaches provide functional insights beyond measures of species richness, detecting community-level responses to disturbance that encompass both convergence and divergence mechanisms. The synergistic interaction between fire and habitat loss indicates that these disturbances cannot be treated as independent drivers of functional change, necessitating integrated consideration of their combined effects in predicting community responses. The maintenance of functional integrity in fire-susceptible tropical forests requires concurrent management of fire regimes and habitat conservation, as neither can be effectively addressed in isolation without compromising the broader functional capacity of bird communities.