Effects of Small Habitat Size and Isolation on the Population Structure of Common Wetland Species

Abstract

Abstract: Habitat fragmentation may cause plant species to suffer from inbreeding and genetic drift, which affects population viability negatively. Less viable populations may contain an altered population structure, i.e., they have a smaller proportion of seedlings and a larger proportion of vegetative adults, when compared to large extensive populations. We applied a hierarchical‐spatial field design, consisting of large habitat islands with surrounding near and distant small habitat islands to distinguish between the two components of habitat fragmentation, i.e., the effect of small habitat size and the effect of isolation. We studied two common habitat‐specific species: Carex davalliana (Cyperaceae) and Succisa pratensis (Dipsacaceae). We identified a decrease in the proportion of C. davalliana seedlings and an increase in the proportion of vegetative tillers in response to isolation. In S. pratensis, we identified a decrease in the proportion of seedlings and an increase in the proportion of vegetative rosettes that were attributable to small habitat size. Hence, we confirmed alterations in the population structure of those common species, although both species were affected by a different component of habitat fragmentation. The observed discrepancy between species could be related their life history. We conclude that habitat fragmentation adversely affects not only rare but also common species. Their loss of viability can inevitably lead to alterations in vegetation structure and consequently lead to the further loss of this species‐rich and threatened ecosystem type.