Results obtained with occurrence and physiological state approaches substantially diverge, which highlights the need to also investigate proximal processes to deeply understand how populations are threatened by landscape modifications. Our study showed that occurrence was negatively affected only by habitat availability at the largest spatial scale whereas the both physiological state indicators studied at the population scale are significantly altered by both habitat availability and fragmentation at the finest spatial scale. We evaluated the effects of both habitat availability and fragmentation at three spatial scales on both the occurrence and two “physiological state” indicators (body condition and level of stress hormone) reflecting the physical state of common toads (Bufo bufo). However, the classical use of occurrence or abundance data as proxy to assess the responses of populations could be insufficient to detect less drastic impacts than short-term population extinction. Disentangling their relative effects is of crucial importance to adequately manage landscapes. Therefore, capital and income breeding may be consequences of both life-history and environmental constraints on foraging success, rather than strategies of reproductive allocation.Īvailability and fragmentation of habitat are today identified as key determinants of population maintenance. The results obtained in the present study suggest that proportional utilization of income or capital depends on the frequency and timing of foraging success during reproductive events. The lack of among-species differences suggests that all species allocated income amino acids to vitellogenesis. Yolks and post-ovulatory scales of labelled females were significantly more enriched in 15N than those of unlabelled females in all species, indicating significant assimilation and allocation of income-derived amino acids to the yolk during vitellogenesis. Scale samples taken at ovulation were used to determine whether snakes assimilated 15N-labelled-leucine from labelled diets. Maternal scale samples taken before labelling were used to estimate endogenous 15N concentrations, which should represent ‘capital’.
After ovulation, we measured yolk 15N p.p.m. We fed 15N-labelled L-leucine to experimental females of each species during vitellogenesis, whereas control females were fed unlabelled meals. We examined the abilities of five viviparous snake species to allocate income to follicles during vitellogenesis. Snakes are considered capital breeders because they efficiently store large amounts of nutrients and energy, potentially enough to support an entire reproductive bout without feeding. Capital breeders have been defined as species that allocate stored reserves to reproduction, whereas income breeders have been defined as species that allocate relatively recently-ingested food resources to reproduction. Reproductive allocation strategies have been historically described as lying on a continuum between capital and income breeding. Since the Gran Chaco forest, a key habitat to the species’ reproduction, is largely threatened, strong conservation action is needed to halt and reverse forest loss in this region. We encourage resource managers to evaluate sensitive reproductive life-history parameters as well as habitat deterioration to asses the conservation status of the populations of the Argentine boa constrictor. Therefore, our study shows that forest loss could enhance vulnerability to extirpation through constraints placed on reproduction. Matting aggregations are scarce in shrublands. We also found that the spatial pattern of vegetation influences the distribution of females and males in the landscape. The obtained results indicate that habitat loss may affect body condition, clutch size and testicular volume of the Argentine boa constrictor. Landscape changes were assessed by analyzing satellite imagery and reproductive parameters were determined by ultrasound images of the reproductive structures. Therefore, we evaluated the effects of forest loss and landscape composition on the reproductive life-history parameters. Because the Gran Chaco is largely threatened due to habitat loss it is necessary to know how landscape changes influence this species. Boa constrictor occidentalis is an endangered species and has a special conservation value since it is endemic of dry forests in the Gran Chaco region. However, the way in which changes in landscape patterns influence intraspecific ecological processes is not completely understood. Many wild reptile species are threatened by habitat loss.
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