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Martin Westgate

Research Fellow
Fenner School of Environment & Society
Australian National University


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Habitat amount versus connectivity: an empirical study of bird responses.

DB Lindenmayer, BC Scheele, MJ Westgate, W Blanchard, CN Foster, J Stein, M Crane, D Florance (In press) Biological Conservation

First published 2020-01-01

Abstract

Habitat loss is widely acknowledged as a key driver of global biodiversity decline. However, whether biodiversity loss occurs in response to reductions in habitat amount versus reduced connectivity in fragmented landscapes is widely debated. A major challenge in resolving this issue is that measures of the amount of native woody vegetation cover and those calculated for connectivity are often highly correlated. Here, using multi-season detection-occupancy models we address the question: After accounting for the effects of native woody vegetation cover, what is the contribution of connectivity to site occupancy, site persistence and site colonization by birds? To answer this question, we constructed milti-season detection-occupancy models for 44 individual bird species based on long-term field surveys in the temperate woodlands of eastern Australia. We found responses to vegetation amount were far more prevalent than responses to connectivity (35 vs 6 species across all analyses of site occupancy, site persistence and site colonization). Responses to vegetation amount were more common for site occupancy (17 species; 12 positive, five negative) than for site persistence (eight responses; seven positive, one negative) and site colonization (seven species, all positive, including three species of conservation concern). Few species exhibited similar occupancy, persistence or colonization responses to vegetation amount, to connectivity, or both. This suggests that vegetation cover and connectivity have different effects on the different processes of occupancy, persistence and colonization. The predominance of vegetation amount effects in our study, and particularly positive effects of vegetation amount for a range of species of conservation concern, suggest the critical importance of both conserving existing areas of native vegetation cover and increasing the amount of that cover. At least for birds, efforts to physically connect particular patches may have relatively less benefit compared to programs to boost overall vegetation cover.

tags: landscape_ecology