Use of Stress‐Hormone Levels and Habitat Selection to Assess Functional Connectivity of a Landscape for an Amphibian

Abstract

The influence of landscape matrix on functional connectivity has been clearly established. Now methods to assess the effects of different land uses on species' movements are needed because current methods are often biased. The use of physiological parameters as indicators of the level of resistance to animal movement associated with different land uses (i.e., matrix resistance) could provide estimates of energetic costs and risks to animals migrating through the matrix. To assess whether corticosterone levels indicate matrix resistance, we conducted experiments on substrate choice and measured levels of corticosterone before and after exposure of toads (Bufo bufo) to 3 common substrates (ploughed soil, meadow, and forest litter). We expected matrix resistance and hormone levels to increase from forest litter (habitat of the toad) to meadows to ploughed soil. Adult toads had higher corticosterone levels on ploughed soil than on forest litter or meadow substrates. Hormone levels did not differ between forest litter and meadow. Toads avoided moving onto ploughed soil. Corticosterone levels in juvenile toads were not related to substrate type; however, hormone levels decreased as humidity increased. Juveniles, unlike adults, did not avoid moving over ploughed soil. The difference in responses between adult and juvenile toads may have been due to differences in experimental design (for juveniles, entire body used to measure corticosterone concentration; for adults, saliva alone); differences in the scale of sensory perception of the substrate (juveniles are much smaller than adults); or differences in cognitive processes between adult and juvenile toads. Adults probably had experience with different substrate types, whereas juveniles first emerging from the water probably did not. As a consequence, arable lands could act as ecological traps for juvenile toads.

Movement in the matrix: substrates and distance‐to‐forest edge affect postmetamorphic movements of a forest amphibian

“…), physiological factors such as stress‐hormone levels (Janin et al. ), microclimate (Rittenhouse et al. ), and predation risk (Pittman et al.…”

Assessing the physiological sensitivity of amphibians to extreme environmental change using the stress endocrine responses

“…For example, adult Bufo bufo experimentally exposed to substrates that vary according to land use practice avoid ploughed soil and enhance salivary CORT when confined to this soil, in comparison with forest litter or meadows (Janin et al 2012). Similarly, salamanders (Ambystoma maculatum) that migrated over pavement also showed higher plasma CORT than individuals that migrated through undisturbed forest (Homan et al 2003).…”

“…Moreover, stress-related physiological variables may anticipate population declines and, consequently, be effective tools in conservation management. For example, this approach has been applied in the context of functional connectivity in amphibian populations exposed to fragmented landscapes (Janin et al 2012). More generally, global patterns of amphibian decline are due to interacting factors, including anthropogenic stressors such as habitat loss, climate change, invasive species, pollution, and skin pathogens such as the fungus Batrachochytrium dendrobatidis (Bd) or iridoviruses from the genus Ranavirus (Stuart et al 2004, Rollins-Smith 2009.…”

Exotic Fish in Exotic Plantations: A Multi-Scale Approach to Understand Amphibian Occurrence in the Mediterranean Region

“…During migration or dispersal, the preference for occupied ponds by conspecifics is common [30]. However, migration and dispersal are species- and individual-specific and influenced by the ability to overcome predation, challenging microclimatic conditions and the resistance to movements of the substrates [32–34]. For instance, clearcut areas may be more difficult to cross due to exposure to more extreme weather conditions and lack of refuge than habitats with vegetation cover [35].…”