Amphibian decline, pond loss and reduced population connectivity under agricultural intensification over a 38 year period

Abstract

Habitat loss, together with less obvious land-use changes such as intensified farming practice, can have significant adverse impacts on biodiversity. An important factor in determining the ability of species to cope with such changes is their potential to sustain a populations network by dispersal across the landscape. Habitat quality and structure are particularly important for surface-dwelling species with low dispersal abilities, such as amphibians. To assess this ecological function, ponds in a coastal and typically rural area of northern France were surveyed for amphibians in 1974, 1992 and 2011. These repeated surveys yielded different outcomes for different species groups. Three rare species persisted in more or less specialized habitat types. Two moderately common species declined, but kept strongholds in coastal dunes and associated marshes. Five common species with broad ecological niches remained equally widespread. The Northern crested newt declined markedly and the Midwife toad declined dramatically, as did their breeding habitats in vegetated ponds and cattle drinking troughs. One species, the Moor frog, may have gone locally extinct. A model of relative resistance to amphibian dispersal was created for different landscape types, on a scale from 0 (low resistance) to 1 (high resistance). This generated values of 0.23 for pasture, 0.72 for arable and 0.98 for urban and transport. As pasture declined in the study area, while arable and urban/transport infrastructure increased, amphibian dispersal became more difficult. However, dispersal paths proved difficult to evaluate in a patchy landscape like the one surveyed, due to a paucity of spatial 123Biodivers Conserv (2017) 26:1411-1430 DOI 10.1007/s10531-017-1307 signal. Pond loss is a more tractable reason for the observed amphibian species decline than is the quality of intervening terrestrial habitat matrix. In 2011, 22 newly created ponds had species richness in line with pre-existing ponds and this will have counteracted a dwindling metapopulation structure, indicating that habitat creation/restoration can play a valuable role in conservation. The colonization of new ponds may also prove more informative for gauging the potential for amphibian dispersal in the landscape than the preceding decline.

Traditionally managed landscapes do not prevent amphibian decline and the extinction of paedomorphosis

“…, Ferreira and Beja , Arntzen et al. ). In many cases, the remaining aquatic habitats became less favorable for the establishment of native aquatic fauna (Ficetola et al.…”

“…, Arntzen et al. ), and paedomorphic newts have suffered particularly dramatic population losses (Denoël et al. ).…”

Amphibians in agricultural landscapes: the habitat value of crop areas, linear plantings and remnant woodland patches

“…Amphibians are one of the most at‐risk groups of taxa in agricultural areas (Cushman, ; Arntzen et al ., ) due to their complex life‐history and narrow habitat tolerances, which can make them susceptible to rapid changes in habitat and microclimate (Cushman, ; Barrett & Guyer, ; Cogger, ). Consequently, many amphibians are threatened with extinction worldwide, more so, than any other vertebrata (Wake & Vredenburg, ; Thompson et al ., ).…”

Twenty‐nine years of population dynamics in a small‐bodied montane amphibian

“…, Arntzen et al. ), yet few studies are large enough in sample size and time frame to adequately address climate (using weather‐related covariates as representatives of climate). In addition, sampling amphibians is difficult and sampling variation is often a high proportion of total variation in demographic estimates used to identify trends, thus further confounding our ability to identify declining populations with confidence (Pechmann and Wilbur , Shaffer et al.…”

“…Identifying population declines is challenging in amphibians because most populations are characterized by large fluctuations in abundance in response to changes in environmental conditions (high process variation; Alford and Richards 1999). Despite the difficulty, previous studies have identified various environmental factors, including weather and climate, as contributors to decline (Daszak et al 2005, Arntzen et al 2017), yet few studies are large enough in sample size and time frame to adequately address climate (using weather-related covariates as representatives of climate). In addition, sampling amphibians is difficult and sampling variation is often a high proportion of total variation in demographic estimates used to identify trends, thus further confounding our ability to identify declining populations with confidence (Pechmann and Wilbur 1994, Shaffer et al 1998, Whiteman and Wissinger 2005.…”