ABSTRACT
Dispersal patterns of third, fourth and fifth instar nymphs of the stenoecious gryllid, Brachytrupes megacephalus (Lefèbvre, 1827), are investigated on the sand dune within the Ghadira Nature Reserve, a remnant habitat patch forming part of the core area that supports the largest population of the species in Malta. Field investigations were carried out over a period of 11 weeks during a specific 75 minute time window, when nymphs are known to engage in subaerial activity at the mouth of their respective burrow. Climatic variables are examined in relation to abundance, while dispersal patterns are presented. The study shows that the predominant movement of nymphs across the terrain is northward, mainly to the northwest and the north-northeast. The present contribution also provides a summary of recommendations for conservation of the species, including an interdisciplinary approach to habitat management at multiple spatial scales.
ABSTRACT
Real-time observation of adaptive evolution in the wild is rare and limited to cases of marked, often anthropogenic, environmental change. Here we present the case of a small population of reed warblers (Acrocephalus scirpaceus) over a period of 19 years (1996-2014) after colonizing a restored wetland habitat in Malta. Our data show a population decrease in body mass, following a trajectory consistent with a population ascending an adaptive peak, a so-called Ornstein-Uhlenbeck process. We corroborate these findings with genetic and ecological data, revealing that individual survival is correlated with body mass, and more than half of the variation in mean population fitness is explained by variation in body mass. Despite a small effective population size, an adaptive response has taken place within a decade. A founder event from a large, genetically variable source population to the southern range margin of the reed warbler distribution likely facilitated this process.