Abstract
Ecologically similar sympatric species, subject to typical environmental conditions, may be expected to exhibit synchronous temporal fluctuations in demographic parameters, while populations of dissimilar species might be expected to show less synchrony. Previous studies have tested for synchrony in different populations of single species, and those including data from more than one species have compared fluctuations in only one demographic parameter. We tested for synchrony in inter-annual changes in breeding population abundance and productivity among four tern species on Coquet Island, northeast England. We also examined how manipulation of one independent environmental variable (predator abundance) influenced temporal changes in ecologically similar and dissimilar tern species. Changes in breeding abundance and productivity of ecologically similar species (Arctic Sterna paradisaea, Common S. hirundo and Roseate Terns S. dougallii) were synchronous with one another over time, but not with a species with different foraging and breeding behaviour (Sandwich Terns Thalasseus sandvicensis). With respect to changes in predator abundance, there was no clear pattern. Roseate Tern abundance was negatively correlated with that of large gulls breeding on the island from 1975 to 2013, while Common Tern abundance was positively correlated with number of large gulls, and no significant correlations were found between large gull and Arctic and Sandwich Tern populations. Large gull abundance was negatively correlated with productivity of Arctic and Common Terns two years later, possibly due to predation risk after fledging, while no correlation with Roseate Tern productivity was found. The varying effect of predator abundance is most likely due to specific differences in the behaviour and ecology of even these closely-related species. Examining synchrony in multi-species assemblages improves our understanding of how whole communities react to long-term changes in the environment and suggests that changes in predator abundance may differentially affect populations of sympatric seabird species.
Highlights
Synchronous temporal variations in demographic parameters have been documented among different populations of single species [1,2,3,4,5]
Our results show that changes in annual breeding population abundances of Arctic, Common and Roseate Terns on Coquet Island were synchronous between 1975 and 2013, but there was no synchrony in breeding abundances of Arctic, Common, Roseate and Sandwich Terns
This suggests that temporal variations in Sandwich Tern breeding abundance were not synchronous with those of other tern species breeding on Coquet
Summary
Synchronous temporal variations in demographic parameters have been documented among different populations of single species [1,2,3,4,5]. In the limited number of studies examining synchrony in more than one species, variation in only a single demographic parameter, such as population abundance, has been analysed [6], [7], [10], [11]. While during periods of extreme environmental change species with disparate ecological niches have been shown to exhibit synchronous population fluctuations [14], in typical conditions ecologically similar species with similar foraging and breeding behaviour might be expected to respond in the same way to changes in the environment compared with ecologically dissimilar species [15,16,17,18]
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