Effects of habitat fragmentation

Habitat fragmentation is a ubiquitous phenomenon in today`s world. Harvester ants are keystone species. The European harvester ant Messor structor is restricted to near-natural, dry grassland, a type of habitat heavily fragmented in Lower Austria. Colonies of this species can contain one or more queens (monogyny vs. polygyny) and the queens vary in size (queen polymorphism). Six hypotheses are posed to describe the potential effects of habitat fragmentation on Messor structor populations with respect to population structure, dispersal strategy, queen number and morphological variations of individuals. They include the reduction of genetic variation within the population, the occurrence of inbreeding, an increased production of small gynes, an increased frequency of polygynous colonies and reduced vs. increased morphological variation of workers, gynes and males (competing hypotheses). An interdisciplinary approach is proposed to test the above hypotheses. This involves a combination of field methods (assessing nest densities, GPS mapping of populations), molecular methods (sequencing of mtDNA and determination of microsatellite allele frequencies), morphology (dissection of gynes, morphometry of workers, gynes and males) and advanced statistical analyses (computation of phylogenetic diversity indices, statistical parsimony network, nested clade analysis, maximum likelihood gene flow analysis). Beyond merely improving our basic ecological knowledge, the results of this study will foster practical conservation measures.

The project reveals that harvester ants that were formerly identified as Messor structor indeed comprise up to six cryptic species. Based on the clarification of the harvester ant`s life history in Lower Austria, multidisciplinary analyses indicate that habitat fragmentation causes genetic isolation, inbreeding, and increased bilateral asymmetry. The harvester ant is a keystone species in dryland ecosystems and the findings are of relevance for conservation management. - It had been a dogma for a long time that all Central European harvester ants belong to one species, Messor structor. In the course of this project a synthetic approach revealed cryptic biodiversity within this ant. While this finding delayed progress with respect to the original questions, it toppled the dogma and facilitated a correct interpretation of the other data obtained in the frame of the project. - Observations on the life history of Messor sp. revealed that colonies contain more than one queen. Further, aggression between single colonies of a population was completely absent. The ant does not perform nuptial flight, mates inside the nests and produces one generation of sexuals per year. - The effects of habitat fragmentation were analysed by means of ecological genetics and morphology. Considering life history data in the interpretation of the data, habitat fragmentation leads to genetic isolation resulting in small inbreeding populations. This reduced genetic variation in isolated populations results in increased bilateral asymmetry.