Abstract
Current rates of wildlife habitat loss have placed increasing demands on managers to develop, validate and implement tools aimed at improving our ability to evaluate such impacts on wildlife. Here, we present a case study conducted at the Natural Area of Doñana (SW Spain) where remote sensing and stable isotope (δ13C, δ15N) analyses of individuals were combined to unravel (1) the effect of variations in availability of natural food resources (i.e. from natural marshes) on reproductive performance of a Slender-billed Gull (Chroicocephalus genei) population, and (2) the role of two adjacent, artificial systems (a fish farm and saltmines) as alternate anthropogenic feeding areas. Based on long-term (1983–2004) remote-sensing, we inferred the average extent of flooded area at the marshland (a proxy to natural resource availability) annually. Estimated flooded areas (ranging from extreme drought [ca. 151 ha, 1995] to high moisture [15,049 ha, 2004]) were positively related to reproductive success of gulls (estimated for the 1993–2004 period, and ranging from ca. 0 to 1.7 fledglings per breeding pairs), suggesting that habitat availability played a role in determining their reproductive performance. Based on blood δ13C and δ15N values of fledglings, 2001–2004, and a Bayesian isotopic mixing model, we conclude that saltmines acted as the main alternative foraging habitat for gulls, with relative contributions increasing as the extent of marshland decreased. Although adjacent, anthropogenic systems have been established as the preferred breeding sites for this gull population, dietary switches towards exploitation of alternative (anthropogenic) food resources negatively affected the reproductive output of this species, thus challenging the perception that these man-made systems are necessarily a reliable buffer against loss of natural feeding habitats. The methodology and results derived from this study could be extended to a large suite of threatened natural communities worldwide, thus providing a useful framework for management and conservation.
Highlights
Human activities are impacting ecosystems globally to an unprecedented degree, leading to increasing rates of natural habitat loss [1]
The connection between resource availability and population dynamics is likely mediated through the acquisition of resources and their allocation to one of the main components of animal fitness such as reproduction [33,34]
Studies aimed at comparing how animals acquire resources and their consequences for population breeding performance during periods of contrasting resource availability will be informed by an understanding of the impact of global environmental change on wild populations
Summary
Human activities are impacting ecosystems globally to an unprecedented degree, leading to increasing rates of natural habitat loss [1]. Coastal zones are of particular concern, since centuries of human influence have resulted in loss and degradation of more than 65% of natural habitats [2]. Remote sensing data is available from the last thirty years, providing valuable information on changes in habitat extent and heterogeneity at long spatial and temporal scales [3,4], and resulting in a powerful tool for investigating the relationship between habitat loss or fragmentation on population dynamics of species [5,6,7]. Several man-made structures, such as solar saltmines, fish farms or rice fields can provide complementary or alternate foraging areas for wild species naturally inhabiting and feeding on intertidal and estuarine systems when natural habitat loss occurs [9,10]. Our ability to monitor spatiotemporal variations in the use of these alternate habitats by wildlife is crucial for accurate assessments of the impact of habitat loss on wild populations
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