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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Authors: | Laurie B Marczak John S Richardson |
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Institution: | (1) Department of Forest Sciences, University of British Columbia, 3041-2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada |
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Abstract: | 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. |
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Keywords: | Aquatic– terrestrial interactions Subsidy timing Compensatory growth Life history phenology Tetragnatha versicolor |
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