Dispersal capability in a habitat specialist bush cricket: the role of population density and habitat moisture

Abstract

1. In fragmented landscapes many insect species depend on a regular exchange of individuals between subpopulations to ensure the persistence of the population. Thus, the ability to disperse is of particular relevance.2. However, in some insect species mobility is not a fixed trait. Hence, knowing the causes of phenotypic plasticity is of great importance when evaluating whether a species is able to survive in fragmented landscapes or not.3. A multi-year field study was conducted to identify possible causes of macroptery in the wing-dimorphic habitat specialist Metrioptera brachyptera L. and to quantify its dispersal capability (% macropters). Therefore, 746 individuals of the species were caught on 135 plots. Additionally, environmental variables that possibly induce the development of macropters (population density and habitat moisture) were recorded.4. Dispersal capability of M. brachyptera was very low. Less than 3% were long-winged. The statistical analysis revealed that the proportion of long-winged M. brachyptera was strongly correlated with high bush-cricket densities and not with habitat moisture. 5. The low dispersal capability of M. brachyptera leads to the conclusion that individual exchange between isolated populations is limited or even impossible. Habitat specialists, like M. brachyptera, may thus be unable to respond to rapid changes in the availability of suitable habitats by dispersing, and hence may be especially dependent on habitat management activities that promote the long-term stability of existing habitat patches.

The role of macropters during range expansion of a wing-dimorphic insect species

“…Our findings are The goodness-of-fit of the model can be derived from the Pseudo R 2 (Nagelkerke's). For more information and sampling design, see Table 1 Evol Ecol (2012) 26:759-770 767 consistent with the idea that macroptery results from both density stress, as has been shown for other wing-dimorphic species (Ando and Hartley 1982;Higaki and Ando 2003;Fartmann 2009, 2011c), and a change in the genetic predisposition to become macropterous (i.e. it is a combination of both ecological and evolutionary effects).…”

“…Denno et al 2001;Matsumura and Suzuki 2003;Poniatowski and Fartmann 2011c) between populations with different colonisation histories, we studied 43 populations of M. roeselii. Only populations with high abundances were chosen as these are more likely to produce macropters (Higaki and Ando 2003;Fartmann 2009, 2011b, c).…”

“…Poniatowski and Fartmann (2011b) attributed this to rising temperatures in spring due to global warming, as favourable (warm/dry) weather conditions promote high population densities at high latitudes that in turn lead to a greater proportion of macropters as a consequence of density stress. However, in addition to the theory of a density-induced macroptery (Higaki and Ando 2003;Fartmann 2009, 2011c), there is also evidence that wing dimorphism is a result of genotypic variation or a combination of both genetic and environmental effects (Harrison 1980;Zera and Denno 1997).…”

“…The ecological relevance of macropterous individuals depends not only on their capability to fly, but also on their frequency (Poniatowski and Fartmann 2011c). Gardiner (2009) observed a significant increase in the sightings of macropterous bush crickets since 1980.…”

“…The clear association between macroptery and dispersal in M. roeselii (Simmons and Thomas 2004;Gardiner 2009;Hochkirch and Damerau 2009) allowed us to use the proportion of long-winged individuals as a reliable index of dispersal capability (cf. Denno et al 2001;Matsumura and Suzuki 2003;Poniatowski and Fartmann 2011c). M. roeselii is an ideal model organism for studying dispersal strategies because dispersing males are easy to detect, regardless of their wing morph, due to their noisy song (Hochkirch and Damerau 2009).…”