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Drivers of amphibian population dynamics and asynchrony at local and regional scales

Citation

Cayuela, Hugo et al. (2020), Drivers of amphibian population dynamics and asynchrony at local and regional scales, Dryad, Dataset, https://doi.org/10.5061/dryad.573n5tb46

Abstract

  1. Identifying the drivers of population fluctuations in spatially distinct populations remains a significant challenge for ecologists. Whereas regional climatic factors may generate population synchrony (i.e., the Moran effect), local factors including the level of density-dependence may reduce the level of synchrony. Although divergences in the scaling of population synchrony and spatial environmental variation have been observed, the regulatory factors that underlie such mismatches are poorly understood.
  2. Few previous studies have investigated how density-dependent processes and population-specific responses to weather variation influence spatial synchrony at both local and regional scales. We addressed this issue in a pond-breeding amphibian, the great crested newt (Triturus cristatus). We used capture-recapture data collected through long-term surveys in five T. cristatus populations in Western Europe.
  3. In all populations – and subpopulations within metapopulations – population size, annual survival and recruitment fluctuated over time. Likewise, there was considerable variation in these demographic rates between populations and within metapopulations. These fluctuations and variations appear to be context-dependent and more related to site-specific characteristics than local or regional climatic drivers. We found a low level of demographic synchrony at both local and regional levels. Weather has weak and spatially variable effects on survival, recruitment and population growth rate. In contrast, density-dependence was a common phenomenon (at least for population growth) in almost all populations and subpopulations.
  4. Our findings support the idea that the Moran effect is low in species where the population dynamics more closely depends on local factors (e.g. population density and habitat characteristics) than on large-scale environmental fluctuation (e.g. regional climatic variation). Such responses may have far-reaching consequences for the long-term viability of spatially structured populations and their ability to response to large-scale climatic anomalies.

Methods

The study was conducted on five populations in France and the United Kingdom using the capture–recapture method. Two populations (POP1 and POP2) are located in southeastern England and are 2.5 km apart and separated from each other by dispersal barriers, such as roads and unsuitable habitat. Another population (POP3) is located in western France. The last two populations (POP4 and POP5) are located in southeastern France. The populations POP2, POP3 and POP4 occupy single breeding sites. POP1 and POP5 are spatially structured populations, both composed of four distinct subpopulations. In POP1, the four subpopulations occupy four distinct ponds, separated from each other by distances ranging from 200 to 800 m. There is a low level of adult movement among subpopulations with dispersal mainly occurring during the subadult phase. In POP5, the four subpopulations occupy four distinct pond groups. Each group was composed of three very close (15-30 m) ponds between which annual dispersal rates are high (<0.20). The pond groups were separated from each other by a distance ranging from 60 to 430 m; the number of breeding dispersal events among pond groups was low (i.e. 12 out of 2282 individuals captured during the period 1996-2015), resulting in a mean dispersal rate of < 0.01. These 12 individuals were discarded from our analyses.

Newts were surveyed over periods ranging from 8 to 20 years between 1995 and 2016. The newts were captured using bottle traps (POP1 and POP2, see Griffiths et al. 2010), funnel traps (POP3), dipnets (POP4) and seine net (POP5). The number of capture sessions performed each year varied from 1 (POP5) to 33 (POP1) during the newt activity period in ponds. Note that in capture-recapture analyses, we merged the observations of intra-annual sessions, considering one single session per year. Newts were individually identified using pit-tags in POP3 and POP5, and by photographs of belly pattern markings in POP1, POP2 and POP4. Providing the image quality is high and the identification is done by trained personnel, belly patterns are a highly reliable method for identifying individual newts. Each individual was classified as adult or juvenile, and adults were sexed on the basis of the presence of a swollen cloaca and a large crest on the back in males. As the number of juveniles was low in our datasets (juveniles only occasionally found in the ponds), the following analyses were restricted to adults.

Usage Notes

No missing values. Contact the first author (Hugo Cayuela, hugo.cayuela@gmail) for additional information.