Abstract
Several factors act on community structure, so determining species composition and abundance patterns. Core processes operating at local scales, such as species-environment matching and species interactions, shape observed assemblages. Artificial habitats (simplified structure) are useful systems for assessing the main factors affecting community composition and disentangling their assembly rules. Drinking troughs (brickwork tanks for free-ranging cattle watering) are widespread in Italy and represent a suitable aquatic habitat for colonization by various aquatic organisms. Dragonflies larvae are usually found in drinking troughs and often exhibit strong species interactions and striking community assembly patterns. Our primary aim was to search for Odonata communities exhibiting non-random co-occurrence/segregation patterns in drinking troughs. We performed null-model analyses by measuring a co-occurrence index (C-score) on larval Odonata assemblages (13 species from 28 distinct troughs). Overall, we found a non-random structure for the studied dragonfly assemblages, which, given their fast generation time, must have been generated by short-term ecological processes (i.e. interspecific interactions). We thus analyzed potential competition/predation among and within ecological guilds. From the field data, we speculated that interactions within the sprawlers’ guild is likely among the main drivers structuring the studied assemblages, especially the effect of intraguild predation between C. erythraea and Sympetrum spp larval stages. We then experimentally tested these interactions in laboratory and demonstrated that intraguild predation among larvae at different development stages may result in an effective exclusion/negative impact on density pattern, representing one of the processes to take into consideration when studying dragonfly assemblages.
Highlights
The species found when surveying assemblages are the result of past and present ecological processes that shape the survival of organisms [1]
Our results demonstrated that the time of hatching may be of importance in structuring dragonfly assemblages because asynchronous development may facilitate the onset of negative interactions [39,40]
The ‘checkerboard arrangements’ resulting in low co-occurrence patterns may correspond to several processes such as: (1) ‘historical checkerboard’ that corresponds to forbidden species pairs caused by different evolutionary or biogeographical histories; (2) ‘habitat checkerboard’ that results from differential affinities for non-overlapping habitats between species; (3) ‘stochastic checkerboard’ arising e.g. from random local extinction and re-colonization events; and (4) ‘competitive or ecological checkerboard’ observed when species pairs are impeded by interspecific interaction exclusion [41]
Summary
The species found when surveying assemblages are the result of past and present ecological processes that shape the survival of organisms [1]. Several factors act on community structure at different levels, determining species composition and abundance patterns. Such patterns were interpreted by Diamond [2] as the results of what he called “assembly rules”. Dragonflies assemblage interactions in artificial habitats community patterns, with the aim (once the rule has been stated) of predicting community change. We can define assembly rules as explicitly stated constraints on community structure that limit which species can belong to locally coexisting subsets of the defined regional species pool. The assemblages that conform to the rules have a greater likelihood of existence, while those that deviate more widely from the assembly rules may exist for shorter time periods but will probably be replaced by assemblages more closely conforming to the constraints over time [1]
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