Relative importance of host plant patch geometry and habitat quality on the patterns of occupancy, extinction and density of the monophagous butterfly Iolana iolas

Abstract

Habitat fragmentation is a major cause of species rarity and decline because it increases local population extinctions and reduces recolonisation rates of remnant patches. Although two major patch characteristics (area and connectivity) have been used to predict distribution patterns in fragmented landscapes, other factors can affect the occurrence of a species as well as the probability of it becoming extinct. In this paper, we study the spatial structure and dynamics of the butterfly Iolana iolas in a 75-patch network of its host plant (Colutea hispanica) to determine the relative importance of patch area, connectivity and habitat quality characteristics on occupancy, extinction and density over the period 2003-2006. Occupancy in 2003, incidence (proportion of years occupied) and probability of extinction were mostly affected by patch area. Smaller patches were less likely to be occupied because they had a higher probability of extinction, partly due to environmental stochasticity. The density of I. iolas was negatively related to patch area in all study years. Only in 2004 was the density of I. iolas positively influenced by fruit production per plant. Our results suggest that for I. iolas, and probably for other specialist butterflies with clearly delimited resource requirements, metapopulation dynamics can be satisfactorily predicted using only geometric variables because most habitat characteristics are subsumed in patch area. However, this hypothesis should be subject to further testing under diverse environmental conditions to evaluate the extent of its generalisation.

The role of habitat quality in fragmented landscapes: a conceptual overview and prospectus for future research

“…Further field evidence confirming Moilanen and Hanski's (1998) results has been reported by Rabasa et al (2008) and Krauss et al (2005). In the latter case, however, the abundance of host plants (resources) was not considered as habitat quality, unlike Grundel and Pavlovic (2007) and Fred and Brommer (2003), and the authors emphasize how the conclusions of Moilanen and Hanski (1998) may depend on the fact that habitat area often correlates with larval food quantity (Krauss et al 2004(Krauss et al , 2005.…”

Drivers of local densities of endangeredLycaena hellebutterflies in a fragmented landscape

“…A positive effect of patch area on immigration probability and its negative effect on emigration rate have often been reported for butterflies (Wahlberg et al 2002;Rabasa et al 2008;Bonelli et al 2013). Consequently, large patches should mostly gain dispersing individuals, whereas the small ones should mostly loose them.…”

Predation risk and patch size jointly determine perceived patch quality in ovipositing treefrogs,Hyla chrysoscelis

“…However, these studies typically manipulate quality while holding size (and isolation) constant and are rarely designed to compare relative importance. However, size and quality are often confounded when concentrations of limiting resources are correlated with habitat area (see review in Haynes and Cronin 2004, Krauss et al 2005, Rabasa et al 2008, thus leaving open the question of which is driving observed patterns. However, size and quality are often confounded when concentrations of limiting resources are correlated with habitat area (see review in Haynes and Cronin 2004, Krauss et al 2005, Rabasa et al 2008, thus leaving open the question of which is driving observed patterns.…”