Ecological niche partitioning and resource utilization in two sympatric lacertid lizard species (Meroles anchietae and M. cuneirostris) from the Namib Desert

Abstract

The ability of two lizard species to co-exist within one habitat requires divergence into one or more niche dimensions (i.e., spatial, temporal and trophic) to reduce competition. Coupled with a scarcity of resources, the Namib Desert is an arid ecosystem with a high lizard diversity and presents an ideal ecosystem to investigate niche partitioning in lizards. In the Namib, fog is the main source of moisture and due to climate change, the Benguela Current which is responsible for most of the climatic patterns on the western coast of Namibia is warming, which could reduce fog production. Biodiversity response to changing climate has been of great concern in many recent studies. Species generally respond to challenges of climate change by shifting their climatic niches along space, time and organismal (i.e., physiology). The present study aimed to assess the nature and extent of genetic and morphological variation between populations of two sympatric lizard species: The shovel-snouted lizard, Meroles anchietae and the wedge-snouted lizard, M. cuneirostris of the Namib Desert in Namibia. The study also investigated the seasonal (autumn and spring) ecological niche differences between populations of the two lizard species, addressed through comparing three niche dimensions (space, time and food), focusing on the significant microhabitat separation of these populations. Seasonal influence of fog on the morphology and thermal biology of populations of the two species was also examined. Sampling in winter was not considered because of low lizard activity, while sampling in summer was not possible due to logistical constraints. Mitochondrial cytochrome b gene sequencing recovered two monophyletic clades within M. cuneirostris, Clade A (comprising of sequences from the central Namib Desert) and Clade B (comprising of sequences from the southern Namib Desert), with a 96% bootstrap support, and one monophyletic clade comprising M. anchietae from the central Namib Desert, Namibia, with a 99% bootstrap support. Although the genetic identity of the two lizard species was confirmed, the results of the molecular analysis suggest further investigations of genetic variation particularly in M. cuneirostris from the southern-most areas of its geographical range. Space niche dimension contributed significantly to the microhabitat separation of M. anchietae and M. cuneirostris (and its associated clades). All three clades indicated a bimodal pattern of activity and an omnivorous diet. The effects of fog were compared between coastal and inland populations of Clade A of M. cuneirostris and M. anchietae. Clade B M. cuneirostris was not considered due to the lack of fog data from the sampled area. The snout to-vent length of the inland M. anchietae was shown to be negatively correlated with the amount of fog. Body temperature of the inland Clade A of M. cuneirostris was also negatively correlated with the amount of fog. The findings of the present study contribute to better understanding of how changes in the desert ecosystems may affect the ecology of lizard species considering consequences of future climate change.