Metapopulation structure and habitat quality in modelling dispersal in the butterfly Iolana iolas

Abstract

Quantifying dispersal is fundamental to understanding the effects of fragmentation on populations. Although it has been shown that patch and matrix quality can affect dispersal patterns, standard metapopulation models are usually based on the two basic variables, patch area and connectivity. In 2004 we studied migration patterns among 18 habitat patches in central Spain for the butterfly Iolana iolas, using mark Árelease Árecapture methods. We applied the virtual migration (VM) model and estimated the parameters of emigration, immigration and mortality separately for males and females. During parameter estimation and model simulations, we used original and modified patch areas accounting for habitat quality with three different indices. Two indices were based on adult and larval resources (flowers and fruits) and the other one on butterfly density. Based on unmodified areas, our results showed that both sexes were markedly different in their movements and mortality rates. Females emigrated more frequently from patches, but males that emigrated were estimated to move longer daily dispersal distances and suffer higher mortality than females during migration. Males were more likely to emigrate from small than from large patches, but patch area had no significant effect on female emigration. The effects of area on immigration rate and the within-patch mortality were similar in both sexes. Based on modified areas, the estimated parameter values and the model simulation results were similar to those estimated using the unmodified patch areas. One possible reason for the failure to significantly improve the parameter estimates of the VM model is the fact that resource quantity and butterfly population sizes were strongly correlated with patch area. Our results suggest that the standard VM modelling approach, based on patch area and connectivity, can provide a realistic picture of the movement patterns of I. iolas .

Patch size and connectivity influence the population turnover of the threatened chequered blue butterfly, Scolitantides orion (Lepidoptera: Lycaenidae)

“…Turnover events took mostly place in patches that are small and isolated, which is in accordance with the chequered blue system in southern Finland (Hanski, 1994;Saarinen, 1995) and with the Karner blue system in the eastern United States (Grundel & Pavlovic, 2007). Other studies on blue butterflies have documented varying importance of area, isolation and host plant density (Thomas et al, 2001;Krauss et al, 2005;Rabasa et al, 2007). Also, it has been suggested that higher connectivity could compensate for lower habitat quality in the small blue metapopulation in -distribution with df = 1.…”

“…This does not mean, however, that host and nectar plants are unimportant as they are the prerequisites for successful reproduction, and have been identified as important determinants of patch occupancy in butterflies (Dennis & Eales, 1997;Thomas et al, 2001;Wahlberg et al, 2002;Krauss et al, 2004Krauss et al, , 2005Binzenhöfer et al, 2007;Grundel & Pavlovic, 2007). Indeed, in this study the host plant number correlated significantly with patch area, although there was large variation in average plant number (see also Krauss et al, 2005;Grundel & Pavlovic, 2007;Rabasa et al, 2007). There is likely to be some minimum number (size of individual plants or density of stems) of Orpines per patch to enable successful reproduction: the larvae of the chequered blue eat the Orpine leaves completely and in very small patches a lack of food may become a problem.…”

“…In any case, the role of the largest islands and subpopulations therein for the long-term metapopulation persistence can only be evaluated via long-term monitoring of the system for which the present study provides a good basis (cf. Rabasa et al, 2007).…”

Different flight behaviour of the endangered scarce large blue butterfly Phengaris teleius (Lepidoptera: Lycaenidae) within and outside its habitat patches

“…Although assessing this aspect of dispersal was beyond the scope of our research, the study by Nowicki and Vrabec (2011) revealed that mortality during the dispersal was fairly low, at maximum 28 % in the year when butterflies numbers peaked above carrying capacity and there was an emigration outbreak, but close to zero in 'normal' years, in a Czech region with both habitat configuration and matrix composition being very similar to those in our study area. The mortality of dispersal is highly dependent on the geometry of the landscape as well as the dispersal biology of the species but several other studies suggested that the mortality during dispersal may be low in butterfly metapopulations (Matter 2006;Rabasa et al 2007;Fric et al 2010; but see Wahlberg et al 2002). Moreover, our estimates of the NSD showed that P. teleius may explore relatively large area in very short time when moving in the matrix.…”

Evolution of sex-biased dispersal: The role of sex-specific dispersal costs, demographic stochasticity, and inbreeding

“…Ralls et al (1980) and Holekamp (1984) report differential costs of dispersal in sperm whales respectively in ground squirrels. Also for species with non-overlapping generations, like insects, there are (to our knowledge) only few published results supporting an asymmetry in dispersal costs (Petit et al 2001;Matter 2006;Rabasa et al 2007). However, we assume that the lack of corresponding evidence is more due to the fact that it has rarely been looked for in empirical research.…”