Spatial structure and nest demography reveal the influence of competition, parasitism and habitat quality on slavemaking ants and their hosts

Abstract

BackgroundNatural communities are structured by intra-guild competition, predation or parasitism and the abiotic environment. We studied the relative importance of these factors in two host-social parasite ecosystems in three ant communities in Europe (Bavaria) and North America (New York, West Virginia). We tested how these factors affect colony demography, life-history and the spatial pattern of colonies, using a large sample size of more than 1000 colonies. The strength of competition was measured by the distance to the nearest competitor. Distance to the closest social parasite colony was used as a measure of parasitism risk. Nest sites (i.e., sticks or acorns) are limited in these forest ecosystems and we therefore included nest site quality as an abiotic factor in the analysis. In contrast to previous studies based on local densities, we focus here on the positioning and spatial patterns and we use models to compare our predictions to random expectations.ResultsColony demography was universally affected by the size of the nest site with larger and more productive colonies residing in larger nest sites of higher quality. Distance to the nearest competitor negatively influenced host demography and brood production in the Bavarian community, pointing to an important role of competition, while social parasitism was less influential in this community. The New York community was characterized by the highest habitat variability, and productive colonies were clustered in sites of higher quality. Colonies were clumped on finer spatial scales, when we considered only the nearest neighbors, but more regularly distributed on coarser scales. The analysis of spatial positioning within plots often produced different results compared to those based on colony densities. For example, while host and slavemaker densities are often positively correlated, slavemakers do not nest closer to potential host colonies than expected by random.ConclusionsThe three communities are differently affected by biotic and abiotic factors. Some of the differences can be attributed to habitat differences and some to differences between the two slavemaking-host ecosystems. The strong effect of competition in the Bavarian community points to the scarcity of resources in this uniform habitat compared to the other more diverse sites. The decrease in colony aggregation with scale indicates fine-scale resource hotspots: colonies are locally aggregated in small groups. Our study demonstrates that species relationships vary across scales and spatial patterns can provide important insights into species interactions. These results could not have been obtained with analyses based on local densities alone. Previous studies focused on social parasitism and its effect on host colonies. The broader approach taken here, considering several possible factors affecting colony demography and not testing each one in isolation, shows that competition and environmental variability can have a similar strong impact on demography and life-history of hosts. We conclude tha...

Nests of red wood ants (Formica rufa-group) are positively associated with tectonic faults: a double-blind test

“…This suite of evidence leads us to propose a hypothesis that drives the observed biological pattern and should be tested in subsequent studies. Previous work has associated microhabitat availability to the spatial structure of ant colonies ( Scharf, Fischer-Blass & Foitzik, 2011 ). In this study system, we argue that the underlying fault lines may be providing a warmer thermal microhabitat, which drives the spatial clustering of RWA colonies.…”

Differential impact of two dominant Formica ant species (Hymenoptera, Formicidae) on subordinates in temperate Europe

“…MacArthur and MacArthur 1961, Hölldobler and Wilson 1990, Tews et al 2004, Ossola et al 2015, intra and interspecific rela tionships, such as competition and social parasitism. The importance of the latter is well known in ants (Savolainen and Vepsäläinen 1988, Hölldobler and Wilson 1990, Andersen 1992, Ryti and Case 1992, Cerdá et al 1997, Czechowski and Markó 2006, Scharf et al 2011, Ślipiński et al 2011, 2014. Colonies of dominant species, espe cially territorial ones, play a crucial role, as organizing centres of the ant community, by limiting the establishment of colonies of subordinate species within dominant territo ries or by managing their accessibility to various resources (Savolainen and Vepsäläinen 1988, Pisarski and Vepsäläinen 1989, Andersen 1992, Bestelmeyer 2000, Lester et al 2010, Cerdá et al 2012.…”

The effects of starvation and repeated disturbance on mass loss, pit construction, and spatial pattern in a trap‐building predator

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