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Spotlight on common lizards – Studland student blog
Restoring mobile sand dunes will increase biodiversity, including threatened vertebrates depending on specific substrates for egg-laying
As sand dunes provide essential habitat, they sustain viable concentrations of notable species, including invertebrates (heath tiger beetle, erratic ant), vertebrates (sand lizards, meadow pipits), plants (marsh clubmoss), and Cladonia spp., comprising of at least 23 distinct lichens at Studland. Out of the six native reptile species present in Great Britain, all of them have established remarkable populations in the Studland dune system. Moreover, governmental regulations and policies have been arranged, in order to protect the conservation status of rare reptiles and the vulnerable habitats on which they considerably depend – in this case, the dune ecosystem. While all rare species are part of the Studland Bay sand dune ecosystem, each of them fulfils a distinct role, and requires particular conservation efforts, in order to survive, and then reproduce during the seasons.
For instance, the bivoltine Hymenoptera require marram grassland and late-flowering plants, such as sea rocket, and also plants with prolonged flowering-cycles, which are present throughout the season (Howe et al. 2010). While the ectothermic lizards should be provided with bare sand via early successional habitats, in order to bask in the sunlight, and control their body temperature, they also require a “kaleidoscope” of habitats, so that they may be able to escape naturally-occurring predators, avoid human disturbance, and prey on the spiders. Thus, restoring the dynamic nature of sand dunes and enabling natural sand movements becomes a conservation management tool for maintaining the intermittently fragmented lizard populations, which burrow their eggs in the bare sand during June-July. The complex pattern of habitats includes lowland dry heathland, with four types of heather, as lizards may shelter in the bell heather, their favourite plant species, and then hunt and forage on small insects.
Lizards are susceptible to habitat fragmentation and loss, which may precede local extinctions
Unlike the sand lizard (Lacerta agilis), the common lizard (Zootoca vivipara) is frequently associated with both heathland and bog habitats. While ericaceous plant assemblages and more than 30% gorse (Ulex europaeus) predominate in the heathland, the boglands include herbaceous vegetation structures, and marsh club moss growing adjacently to carnivorous Drosera spp. Therefore, the wide array of habitats present at Studland (sand dunes, heathland, bogs) provide a thermally-favourable hibernaculum for Z. vivipara, and also a vast range of diverse invertebrates for feeding (Farren-Aodan et al. 2010). The lizards will exploit the most convenient habitat which matches their thermal conditions and egg-laying requirements, and minimizes the predation risk.
Nonetheless, historic habitat fragmentation is a driving force of lizard population reductions. Although in the 1930s there used to be 30% open bare sand at Studland, this percentage has become exclusively 2%. Conservation priorities should aim for microhabitat connection, and soft-release lizard reintroductions, in order to maintain reasonably stable numbers of elusive species and increase the species abundance.
The evolution of life history traits in common lizards involves trade-offs between reproductive and survival success, and the traits highly diverge and alternate depending on the complexity of environmental gradients.
Rutschmann et al. (2016) examined the trade-off between number of offspring versus energy invested for each offspring in natural populations of Z. vivipara females. As the viviparous females only possess a confined amount of energy to invest in their offspring, there must be an intricate trade-off between reproduction and survival. For instance, should female lizards invest more in their survival and produce fewer offspring? Should they invest more in reproduction and thus allocate more resources to their offspring? If the second applies, should the female lizards generate only one or two offspring, which may leave the parental care later? Should the female lizards produce more than three offspring, which may leave the parental care earlier, and thus, the offspring be in a higher quantity? This might increase the lizard population size, and prevent further anthropogenic declines.
It must be considered predation risks may act on the juvenile population, and thus, on the population traits, leading to earlier maturity of lizards, with elevated reproductive success, but a lower lifespan. However, there may be critical perils associated with producing more offspring, such as elevated lizard female mortality. It is exactly this trade-off which must be carefully considered, as a growing body of literature discovered negative correlations between survival and reproduction rates, as the females were not able to maximize synchronously all life-history traits. Nonetheless, several studies have focused on the extent to which life-history traits can be enhanced and thus, trade-offs could be attenuated. Distinct habitats exert distinct selection pressures on the lizard population size, and thus, lizard females may produce fewer offspring, if the juvenile survival is constrained by habitat loss or human disturbance. On the other hand, the females may generate more offspring when encountering high-productivity habitats, with minimum disturbance.
References
Farren-Aodan, N.V., Prodohl, P.A., Laming, P., Reid, N., 2010. Distribution of the common lizard (Zootoca vivipara) and landscape favourability for the species in Northern Ireland. Amphibia-Reptilia, 31 (3), 387-387.
Howe, M.A., Knight, G.T., and Clee, C., 2010. The importance of coastal sand dunes for terrestrial invertebrates in Wales and the UK, with particular reference to aculeate Hymenoptera (bees, wasps, and ants). Journal of Coastal Conservation, 14, 91-102.
Rutschmann, A., Miles, D.B., Clobert, J., Richard, M., 2016. Warmer temperatures attenuate the classic offspring number and reproductive investment trade-off in the common lizard, Zootoca vivipara. Biology Letters, 12, 20160101.