Using non-conspicuous metrics to examine selected impacts of disturbance on a long-lived reptile

Abstract

Loss or disturbance of habitat often results in landscapes being fragmented into a series of isolated remnants varying in size, quality, and conservation value. Habitat disturbance has deleterious consequences for ecosystem processes, but can have varying effects on species persistence. Many deleterious effects on species post-disturbance are obvious, yet some are more subtle and can elude detection in long-lived species. We used more subtle metrics to evaluate populations of endangered iguanas Iguana delicatissima inhabiting disturbed (i.e. low-to moderate-density villages and towns) and non-disturbed areas on the island of Dominica, West Indies. We investigated differences in iguana sex ratios, asymptotic size, characteristic growth rate, body condition, abundance, and densities between our defined disturbed and non-disturbed habitats. Contrary to expectations, there were no statistical effects of disturbed areas on density, sex ratio, body condition, or characteristic growth rates, yet there was a slight positive effect on asymptotic body size for iguanas on Dominica. Despite these results, I. delicatissima is still affected adversely by manifold threats, as evidenced by the continued precipitous declines and local extirpations of the species across its range. Our results do, however, suggest that if factors such as degraded nest sites and killing by non-native mammalian predators are mitigated, then moderately disturbed, human-occupied areas can be managed as corridors or buffer zones for I. delicatissima in an increasingly fragmented landscape.

Favoring recruitment as a conservation strategy to improve the resilience of long‐lived reptile populations: Insights from a population viability analysis

“…Our study provides the first robust estimate of the abundance, adult survival, and recruitment rates of a Lesser Antillean iguana population. Although the density of this species on Chancel Islet (873.03 iguanas/km 2 in 2020) is much higher than in other places (e.g., 35 iguanas/km 2 in St Eustatius) (Debrot et al., 2013 ), it is still far below the highest estimated densities for this species, which can exceed 4,000 iguanas/km 2 under favorable conditions (Knapp & Perez‐Heydrich, 2012 ). Despite the protected status of the islet and the lack of obvious threats to adult survival, the population declined rapidly at a rate of 4% per year, which would lead it to become quasi‐extinct within the next 50 years if drastic action is not taken to reverse the trend.…”

Age‐dependent, negative heterozygosity–fitness correlations and local effects in an endangered Caribbean reptile, Iguana delicatissima

“…We captured free-ranging adult iguanas by noose in the summers of 2007, 2008, and 2009. Earlier summer months coincided with the timing of female migration to communal nesting sites, whereas August and September aligned with the primary hatching period (Knapp & Perez-Heydrich, 2012). Blood was collected by venipuncture of the ventral coccygeal vein using a heparinized syringe and stored in vacutainer tubes with 100 mM Tris, 100 mM Na 2 EDTA, 10 mM NaCl, and 1% SDS at a ratio of 1:2 (Longmire, Maltbie, & Baker, 1997).…”

Hurricane-induced population decrease in a Critically Endangered long-lived reptile

“…Thus, besides gardens, also the periferic habitats of this residential area are important iguana habitats. Indeed, Knapp and Perez-Heydrich (2012) found that biometric variables did not differ between iguanas living in- and outside of gardens. Furthermore, highest iguana abundance was found in the Chionanthus - Nectandra mountain habitat (De Freitas et al 2012), at high (386m) elevation on the volcano, however this habitat was covered by a single transect, thus we lack a perspective of variation.…”