The importance of distance to resources in the spatial modelling of bat foraging habitat

Abstract

Many bats are threatened by habitat loss, but opportunities to manage their habitats are now increasing. Success of management depends greatly on the capacity to determine where and how interventions should take place, so models predicting how animals use landscapes are important to plan them. Bats are quite distinctive in the way they use space for foraging because (i) most are colonial central-place foragers and (ii) exploit scattered and distant resources, although this increases flying costs. To evaluate how important distances to resources are in modelling foraging bat habitat suitability, we radio-tracked two cave-dwelling species of conservation concern (Rhinolophus mehelyi and Miniopterus schreibersii) in a Mediterranean landscape. Habitat and distance variables were evaluated using logistic regression modelling. Distance variables greatly increased the performance of models, and distance to roost and to drinking water could alone explain 86 and 73% of the use of space by M. schreibersii and R. mehelyi, respectively. Land-cover and soil productivity also provided a significant contribution to the final models. Habitat suitability maps generated by models with and without distance variables differed substantially, confirming the shortcomings of maps generated without distance variables. Indeed, areas shown as highly suitable in maps generated without distance variables proved poorly suitable when distance variables were also considered. We concluded that distances to resources are determinant in the way bats forage across the landscape, and that using distance variables substantially improves the accuracy of suitability maps generated with spatially explicit models. Consequently, modelling with these variables is important to guide habitat management in bats and similarly mobile animals, particularly if they are central-place foragers or depend on spatially scarce resources.

Figure 1. Linear distance between the roost and the centre of each foraging area located during this study.

Most of these areas were used on multiple nights by the same bat.

Figure 2. Comparison of the performance between selected models including and excluding distance variables.

The comparison was performed using the area under the ROC curve (AUC). Note the low performance (smaller AUC) of the models that exclude the distance variables, particularly for M. schreibersii (see Table 2 for full model statistics).

Figure 3. Estimated probability of occurrence of foraging bats, based on models using distance to roost and distance to water.

Notice the great power of the two most important distance variables for both species, to explain the probability of occurrence.

Figure 4. Maps of the predicted foraging suitability of the study area for Miniopterus schreibersii (left) and Rhinolophus mehelyi (right).

These maps were drawn according to the best candidate models including (top) and excluding (bottom) distance variables (see models in Table 2). Habitat suitability is shown on a colour scale ranging from 0 (low suitability) to 1 (high suitability).

Figure 5. Location of the study area and representation of a subset of the variables analyzed.

Variables: land-cover (a), distance to roost (b), distance to urban areas (c) and distance to water (d). Darker shades represent higher distances, in the last three variables.