Patch-based graphs of landscape connectivity: A guide to construction, analysis and application for conservation

Graph theory has become a popular tool for modelling the functional connectivity of landscapes. We conduct a review of studies that use graph theory to model connectivity among patches of habitat (patch-based graphs), with the intention of identifying typical research questions and their associated graph construction and analysis methods. We identify and examine nine questions of conservation importance that can be answered with these types of graph models, discussing appropriate applications of these questions and presenting a guide for using graph methods to answer them. We also investigate how the connectivity predictions of patch-based graphs have been assessed and emphasize the importance of empirical evaluation. Our findings identify commonality among diverse approaches and methodological gaps with an aim to improve application and to help the integration of graph theory and ecological analysis.     

Managing landscapes for the little bustard Tetrax tetrax: lessons from the study of winter habitat selection

More than half of the world's population of the little bastard Tetrax tetrax lives in the Iberian Peninsula, where it is mostly dependent for survival on extensive agricultural areas. The species has declined dramatically, chiefly due to changes in agricultural practices, and is now globally ‘Near Threatened’. Knowledge of its habitat requirements is crucial to reverse the trend of habitat deterioration. Winter habitat preferences were studied in a region dominated by extensive cereal farming in Southern Portugal, comparing the characteristics of sites used by 54 flocks with those of randomly selected sites within the study area. The birds preferred recent fallows and grassy vegetation of mid-size (about 11-20 cm) and mid-density (about 11-50% cover). They tended to concentrate on the tops of hills and to avoid disturbed areas near roads and houses. Overall, the observed preferences suggest that predator avoidance is a significant factor in habitat selection. To improve habitat suitability for little bustard, managers of key wintering areas should minimize permanent sources of human disturbance, encourage rotations with frequent fallows, and favour moderate levels of grazing to manipulate vegetation height and cover. Particular attention should be given to the upper parts of the hills.     

The importance of spatial scale for the conservation of tidal flat macrobenthos: An example from New South Wales, Australia

Planners of Marine Protected Areas (MPAs) commonly use maps of habitat types when choosing areas to conserve. This assumes that habitats are homogeneous, and therefore, that any area of habitat will represent the full spectrum of ecological diversity within that habitat. Here, we report that macrobenthic assemblages in tidal flat habitats were spatially heterogeneous in terms of beta diversity (taxonomic turnover), abundance, taxonomic richness and Shannon-Wiener H′ Diversity. Importantly, the patterns of heterogeneity were scale dependent for the three spatial scales we examined; plots (20 m), sites (100s of m) and estuaries (<30 km). The three estuaries in the study were compositionally similar as they shared the same dominant taxa, although one estuary had significantly more taxa and a higher abundance of macrobenthos. Assemblages within tidal flats differed at scales of 100s of m for all ecological measures. Most notably, beta diversity was highest at this scale. Assemblages were relatively more homogeneous at the 20-m scale. These findings highlight the value of examining more than one ecological measure and estimating magnitude of effects across a variety of scales. This work presents two important considerations for MPAs. First, although tidal flats in different estuaries are compositionally similar for dominant taxa, rarer taxa and high heterogeneity in abundance should influence the choice and number of tidal flats in MPAs. Second, strong compositional heterogeneity within individual tidal flats implies that conservation of whole habitat, rather than sections of a tidal flat, is essential if this habitat type is to be used to represent taxonomic diversity.