Disentangling how landscape spatial and temporal heterogeneity affects Savanna birds.

Bronwyn Price,Clive A Mcalpine,John A Ludwig,Stuart R Phinn,Alex S Kutt,Doug Ward,Justin David Brown

doi:10.1371/journal.pone.0074333

Abstract

In highly seasonal tropical environments, temporal changes in habitat and resources are a significant determinant of the spatial distribution of species. This study disentangles the effects of spatial and mid to long-term temporal heterogeneity in habitat on the diversity and abundance of savanna birds by testing four competing conceptual models of varying complexity. Focussing on sites in northeast Australia over a 20 year time period, we used ground cover and foliage projected cover surfaces derived from a time series of Landsat Thematic Mapper imagery, rainfall data and site-level vegetation surveys to derive measures of habitat structure at local (1–100 ha) and landscape (100–1000s ha) scales. We used generalised linear models and an information theoretic approach to test the independent effects of spatial and temporal influences on savanna bird diversity and the abundance of eight species with different life-history behaviours. Of four competing models defining influences on assemblages of savanna birds, the most parsimonious included temporal and spatial variability in vegetation cover and site-scale vegetation structure, suggesting savanna bird species respond to spatial and temporal habitat heterogeneity at both the broader landscape scale and at the fine-scale. The relative weight, strength and direction of the explanatory variables changed with each of the eight species, reflecting their different ecology and behavioural traits. This study demonstrates that variations in the spatial pattern of savanna vegetation over periods of 10 to 20 years at the local and landscape scale strongly affect bird diversity and abundance. Thus, it is essential to monitor and manage both spatial and temporal variability in avian habitat to achieve long-term biodiversity outcomes.

Highlights

Savanna ecosystems are an important reservoir of biodiversity, but are undergoing rapid changes due to increased land use pressures including clearing, grazing and changes in fire regimes [1,2,3]
Models including variables measuring spatial heterogeneity in ground cover and foliage projected cover performed significantly better for woodland bird species diversity and abundance of individual species than those including temporal variability in rainfall but assuming spatial homogeneity across 5-km grid cells
This study advances our understanding of the relative importance of landscape spatial and temporal heterogeneity on fauna populations in highly dynamic environments such tropical savannas

Summary

Introduction

Savanna ecosystems are an important reservoir of biodiversity, but are undergoing rapid changes due to increased land use pressures including clearing, grazing and changes in fire regimes [1,2,3]. Annual and inter-annual variability in rainfall can have a dramatic impact on ecosystems and their biota [4,5,6]. Seasonal and inter-annual variability in habitat attributes such as cover and resource availability are important components of species’ habitat relationships, and can have an important influence on species’ distribution patterns according to their mobility and ability to utilize changing habitat resources [7], [11]. While multi-temporal analysis has been widely applied to quantify landscape change [12], [13], few studies have quantified the relative importance of temporal heterogeneity in habitat attributes on fauna distribution and abundance

Methods

Results

Discussion

Conclusion