Growth and development rates in a riparian spider are altered by asynchrony between the timing and amount of a resource subsidy
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Rapid growth in response to increased prey abundance may be induced by environmental variability associated with resource subsidies. Spiders living in riparian areas are subject to frequent, episodic bursts of aquatic prey (subsidies). These periods of high resource abundance may occur at different points in recipient consumers’ development through variation in emergence patterns of prey between years or across a landscape. We examine how variable timing of subsidy abundance intersects with life history scheduling to produce different growth and development outcomes for individuals within a population. Through a series of controlled feeding experiments, we tested the hypotheses that the spider Tetragnatha versicolor: (1) exhibits compensatory growth in response to subsidy variability, (2) that rapid increases in mass may result in a greater risk of mortality, and (3) that the timing of subsidy resources relative to the development schedule of this spider may produce different outcomes for individual growth patterns and adult condition. Spiders fed at very high rates grew fastest but also showed evidence of increased mortality risk during moulting. T. versicolor is capable of exhibiting strong growth compensation—individuals suffering initial growth restriction were able to catch up completely with animals on a constant diet utilising the same amount of food. Spiders that received an early pulse of resources (simulating an early arrival of an aquatic insect subsidy to riparian forests) did worse on all measures of development and fitness than spiders that received either a constant supply of food or a late pulse of resources. Importantly, receiving large amounts of food early in life appears to actually confer relative disadvantages in terms of later performance compared with receiving subsidies later in development. Subsidies may provide greater benefits to individuals or age cohorts encountering this resource abundance closer to the onset of reproductive efforts than subsidies arriving early in development.
KeywordsAquatic–terrestrial interactions Subsidy timing Compensatory growth Life history phenology Tetragnatha versicolor
The authors acknowledge assistance with rearing and feeding spiders from Kyle Bateson and Nancy Hofer; Kelly Walker assisted with the analysis of spider body compounds. Members of the Stream and Riparian Research Lab at the University of British Columbia provided valuable feedback on early versions of the manuscript. The manuscript was also substantially improved by comments from several anonymous reviewers. This project was funded in part by the Natural Sciences and Engineering Research Council of Canada and the Forest Sciences Program (British Columbia—Forest Investment Account). All experiments comply with current laws in Canada.
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