Habitat background selection by colonizing intermittent pond invertebrates

Abstract

Habitat selection processes by organisms colonizing freshwater bodies have not been commonly studied, despite their obvious relevance to wetland ecology and management. We monitored, weekly, all organisms that appeared in tanks with different backgrounds (brown; white) and substrate/food availability treatments (control; added leaf litter; added algae) floating on the water surface of a natural intermittent pond. The experiment lasted for 14 weeks, from pond filling to pond drying, during which time we collected around 9,000 colonizing insects per m² (e.g., Diptera, Coleoptera, Hemiptera, and eggs) and a similar number of colonizing non-insects (e.g., Acari, Crustacea, Gastropoda, and ephippia). Non-insects exhibited greatest colonization early in the hydroperiod, correlated with major rain-fall events. Insect colonization was low at first, peaked in late May, and thereafter remained high until the pond dried. Most ovipositing female insects (especially chironomids) were attracted to tanks with a dark background or those containing decomposing dark leaves, although there were exceptions related to taxon (e.g., beetles) and hydroperiod. Non-insects showed treatment preferences similar to the insects, with cladoceran ephippia appearing more in the Leaf treatment. Colonization mechanisms were deemed ‘active’ for insects and largely ‘passive’ for the microcrustaceans, and the various possibilities for the latter (heavy rainfall, wind, wildlife) are discussed. For highly dispersive taxa, such as adults of the beetles Helophorus sp. and Anacaena sp. colonization densities at the pond surface were calculated to attain maxima of around 26 and 33 m⁻² respectively, in early May.