Patterns of distribution and landscape connectivity of the stag beetle in a human-dominated landscape

Abstract

Urbanisation and the spread of agriculture have resulted in high levels of forest loss, habitat fragmentation and degradation in many regions of the world. In Italy, the Po Plain is the most human-dominated landscape of the country and, after decades of exploitation, old-growth forests have been reduced to small and isolated patches, often threatened by invasive tree species such as the black locust (Robinia pseudoacacia). In these habitats, the occurrence of many forest-dependent species is related to the quality and availability of suitable areas, as well as the connectivity between the remaining forested patches.Thus, recently developed species distribution models have been applied, namely the Ensemble of Small Models (ESMs), to identify areas of occurrence for a rare and protected saproxylic beetle species, the stag beetle Lucanus cervus and the inverse of the resulting distribution maps as resistance maps have been used to estimate landscape connectivity for this species.Response curves suggested that the probability of the stag beetle occurrence increased with habitat diversity, grassland coverage and native forests, especially oak and mixed forests. The other forest coverage, such as those with black locust, beech, chestnut and black cherry, showed a unimodal relationship peaking approximately at 70%, 8%, 55% and 13% respectively. The stag beetle occurrence was unimodal related to distance to watercourses and distance to human settlements and negatively related to shrub-lands, croplands, sparse and dense human settlements. Landscape connectivity showed similar patterns, except for oak forest coverage, which showed a negative relationship to landscape connectivity.In conclusion, stag beetles can persist in a human dominated landscape only in the presence of forest patches, including those with black locust trees. It is also inferred that ESMs may be suitable for modelling rare species distributions and estimating landscape connectivity to promote species conservation.

Daily survival and dispersal of adult Rhagonycha fulva (Coleoptera: Cantharidae) in a wooded agricultural landscape

“…1 shows the percentage of individuals (Haslem & Bennett, 2008). Conducting studies on insect dispersal within a semi-natural and linear habitat, specifically a fi eld margin, provides an insight to the quality of the fi eld margins (Diekötter et al, 2008) and could also function as an indicator for how other species may move within that habitat type (Della Rocca et al, 2017).…”

“…It is reasonable to assume that for many species the greater the longevity the greater the capacity to disperse and perhaps the greater resilience a species displays to landscape change (Bubová et al, 2016). There are many studies on the effects of landscape composition and confi g- uration on levels of biodiversity (Della Rocca et al, 2017). Inherent in these studies is that those species with a more limited power of dispersal are more likely to be affected by landscape features, particularly at a local level.…”

Far from the madding crowd: Tolerance toward human disturbance shapes distribution and connectivity patterns of closely related Martes spp.

“…Although ENMs have the benefit of avoiding subjective expert opinions (Milanesi, Holderegger, Caniglia, Fabbri, Galaverni, & Randi, ; Milanesi, Holderegger, Caniglia, Fabbri, & Randi, ; Wang et al, ), which can potentially bias resistance surfaces due to insufficient knowledge about both the ecology of the target species and real distribution of corridors and barriers to its movements in the area of interest (Della Rocca et al, ; Stevenson‐Holt, Watts, Bellamy, Nevin, & Ramsey, ; Zeller, McGarigal, & Whiteley, ), our Geographic Information System (GIS)‐based models inevitably have some limitations and their accuracy should be tested by field data. Particularly, the role played by shrubland and anthropogenic barriers needs to be validated by fine‐scale, radiotracking or fecal DNA‐based studies.…”

“…Following previous studies (Della Rocca, Bogliani, & Milanesi, ; Milanesi et al, ; Milanesi, Holderegger, Caniglia, Fabbri, & Randi, ; Pullinger & Johnson, ; Spear, Balkenhol, Fortin, Mcrae, & Scribner, ; Wang, Yang, Bridgman, & Lin, ), we derived a resistance map for each species, defined as the inverse of the distribution map (1 – probability of occurrence) and combined it with circuit theory to explore landscape connectivity. Circuit theory models movement ecology via random walks across all available pathways, assuming that the intensity of flow between nodes (locations) is proportional to the number of times an individual goes from one node to another moving through the particular cell under consideration (McRae et al, ).…”

“…A current density map was considered independent of node placement when the curve comparing correlation coefficients to the number of node pairs reached an asymptote (i.e., a slope of zero; Koen et al, ; Pitman et al, ). Following Della Rocca et al (), the final current map (i.e., that with the optimal number of random nodes) was rescaled between 0 and 1 (indicating low and high landscape connectivity, respectively). The correlation between the final current maps of the two marten species was assessed by Spearman's correlation coefficient.…”