Species responses of colonising beetles to variation in patch quality, number, and context in experimental aquatic landscapes

Abstract

Increased diversity with increasing habitat area is a well-established ecological pattern. However, habitat selection theory suggests that patch quality rivals area in determining rates of colonisation and resulting community structure. Colonisation by natural populations of aquatic beetles was quantified along gradients of increasing patch number and patch quality. Four circular experimental landscapes, each containing six unique locality types (combinations of number and type of patch), were established using 84 cattle tanks (volume 1000 litres) as patches. Patch quality varied in terms of the presence/absence and spatial proximity of predatory fish, and patch number varied from one to eight patches in each locality. Patch quality significantly affected the colonisation rate of most aquatic beetle species in both major families (Dyticidae and Hydrophilidae), as species avoided patches containing fish and also showed spatial contagion of predation risk by avoiding fishless patches in close proximity to these predators. Effects of patch number were passive, resulting in linear increases in abundance, with rates highly dependent on patch quality. Patch quality may equal or exceed landscape characteristics such as patch number in determining colonisation rate and abundance of colonising beetles, and in generating resulting patterns of species diversity.