31 research outputs found

    SEX AND MICROHABITAT INFLUENCE THE ALLOCATION OF MYCOSPORINE-LIKE AMINO ACIDS TO TISSUES IN THE PURPLE SEA URCHIN, STRONGYLOCENTROTUS PURPURATUS

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    Field surveys of Strongylocentrotus purpuratus demonstrated that concentrations of natural sunscreens, mycosporine-like amino acids (MAAs), were higher in females than males for both gonadal and epidermal tissues, increased in ovaries as spawning season approached, and were influenced by the sea urchins’ microhabitat. Sea urchins occupying burrows, or “pits”, had lower concentrations of MAAs than those outside pits, suggesting a trade-off between physical and UV protection. Overall, UV irradiance did not influence MAA accumulation in gonadal tissues. However, males increased their allocation of MAAs to epidermal tissues in the microhabitat with the highest irradiance. Relative concentrations of individual MAAs were similar for epidermal tissues from both sexes and ovaries, providing broadband UVA/UVB absorbance, but testes contained principally one MAA, palythine. This is the first study to demonstrate that S. purpuratus and eight species of macroalgae in California have MAAs, and that the concentrations can be influenced by microhabitat

    Data from: Prey state alters trait-mediated indirect interactions in rocky tide pools

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    Several studies on trait-mediated indirect interactions (TMIIs) have shown that predators can initiate trophic cascades by altering prey behaviour. Although it is well recognized that individual prey state alters antipredator and foraging behaviour, few studies explore whether this state-dependent prey behaviour can alter the strength of the ensuing tritrophic cascade. Here, we link state-dependent individual behaviour to community processes by experimentally testing whether hunger level and body size of prey altered antipredator behaviour and thus changed the strength of trophic cascades between predators and primary producers. In rocky intertidal tide pools on the California Coast, waterborne cues from the predatory seastar Leptasterias spp. (Stimpson) can cause the herbivorous snail Tegula (Chlorostoma) funebralis (A. Adams) to reduce grazing and flee tide pools, resulting in positive indirect effects on tide pool microalgae. However, we show that the strength of this behaviourally-mediated cascade may be contingent on prey hunger level and body size. During short field experiments at low tide, medium-sized snails that were either newly collected from the field or fed for 1 week in the laboratory mediated strong TMIIs because they grazed less when seastars were present. In contrast, no TMIIs occurred when medium-sized snails had been starved for 1 week because they continued grazing regardless of seastar presence. Newly collected small snails fled from seastars but did not mediate cascades because they ate little algae. Despite reaching an apparent size refuge from predation, many newly collected large snails fled from seastars, but those individuals that remained tended to graze the algae more quickly, resulting in unexpected negative indirect effects of seastars on algae cover. The implication of this pattern for the natural system is unclear. Because average hunger level and size of snails vary over time and space in nature, a mosaic of TMII strength may exist. Overall, the strength of tritrophic TMIIs in tide pools depended on individual prey state, supporting model predictions and adding to sparse empirical evidence. This outcome suggests that patterns occurring system-wide over the long term may be influenced by the state-dependent decisions made by the individuals present

    A unified meta‐ecosystem dynamics model: Integrating herbivore‐plant subwebs with the intermittent upwelling hypothesis

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    Abstract Determining the relative influence of biotic and abiotic processes in structuring communities at local to large spatial scales is best understood using a biogeographic comparative‐experimental approach. Using this approach, previous work suggests that intertidal community dynamics (top‐down and bottom‐up effects) vary unimodally along an upwelling‐based productivity gradient, termed the Intermittent Upwelling Hypothesis (IUH). Evidence consistent with the IUH comes from the sessile invertebrate/predator (SIP) subweb in certain rocky intertidal communities, but whether this pattern extends to macrophyte/herbivore (MH) subwebs is unknown. Here we ask: Are MH subwebs also structured as predicted by the IUH? What is the relative importance of herbivory and predation in structuring these communities? Under what conditions do ecological subsidies like nutrients or propagule production drive community dynamics? And are omnivorous interactions important? We hypothesize that MH subwebs are driven by a new construct, the Grazing‐Weakening Hypothesis (GWH), which states that MH interactions weaken monotonically with increasing nutrients, with strong (weak) herbivory and low (high) macrophyte productivity at low (high) nutrients. We explored local‐to‐large spatial scale dynamics of both subwebs using a biogeographic comparative‐experimental factorial field experiment testing joint and separate effects of herbivores and predators between two continents. Experiments at 10 sites ranging from persistent upwelling to persistent downwelling regimes ran for 26–29 months in Oregon and California, and New Zealand (NZ) South Island. For the MH subweb, results were consistent with the GWH: herbivory declined and macrophytes increased with increasing nutrients. As expected, results for the SIP subweb were consistent with the IUH: predator effect size was unimodally related to upwelling. Overall, herbivory explained more variation in community structure than did predation, especially in NZ. Omnivory was weak, sessile invertebrates outcompeted macrophytes, and ocean‐driven subsidies provided the basic template driving ecosystem dynamics. We propose a unified meta‐ecosystem dynamics model combining MH and SIP results: with increased upwelling, sessile invertebrates and underlying dynamics vary unimodally (as in the IUH), while herbivory decreases and macrophytes generally increase. While this model was based on research in temperate ecosystems varying in upwelling regime, its wider applicability remains to be tested
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