Impact of Flower Harvesting on the Salt Marsh Plant \u3cem\u3eLimonium carolinianum\u3c/em\u3e

Because of the potentially detrimental effects of seed production on adult survivorship and growth, moderate flower harvesting may have little negative impact on population growth of long-lived perennial plants such as Limonium carolinianum (Walter) Britton. We examined this by collecting data on survivorship, growth, and fecundity of an unharvested population over a period of 5 years and conducted a controlled experiment to examine the effect of harvesting on adult survivorship and growth over a 3-year period. Data were summarized in the form of a stage structured matrix population model with a stochastic element that incorporated year-to-year variation in transition probabilities. Contrary to our original hypothesis, we found that preventing seed set through removal of flowers did not increase adult survivorship or growth. By determining the harvest level that reduced population growth rate to 1.0, we estimated the maximum sustainable harvest level to be 16%, a value that is approximately half that of reported harvest levels on accessible marshes in the study area. In spite of this, the reported harvest levels are unlikely to drive local populations to extinction in the foreseeable future. Providing the adult population size is \u3e100 and harvest levels are \u3c90%, time to local extinction will exceed 100 years. This is a function of the very high survivorship of adults in this species and the fact that harvesting has no negative impact on adult survivorship or growth. However, because of the long preadult phase in this species (8–9 years) and the fact that fecundity of young adults is low, recovery from overharvesting is extremely slow. Adult population size can be reduced to 25% of its original value in 7 years at high harvest levels, but it will take 34 years on average to recover once harvesting is terminated

Male amphipods increase their mating effort before behavioural manipulation by trematodes

Certain parasites appear to alter the behaviour of intermediate hosts, making them more susceptible to predation by final hosts (adaptive parasite manipulation). In some cases, however, hosts are expected to respond by increasing their reproductive effort when first parasitized (adaptive host response). We tested predictions of these two hypotheses for males of the amphipod Corophium volutator (Pallas). Consistent with adaptive parasite manipulation, males infected by the trematode Gynaecotyla adunca (Linton) were likely to crawl on the surface of a mud flat, but only when visual predation by the final host, semipalmated sandpipers, Calidris pusilla L., was likely (during the day), and after trematodes had developed to their infective stage. Males appeared to compensate for parasitism by being more likely to mate, and perhaps by increasing ejaculate size. However, parasitized males that mated when first infected were less likely to mate again once their parasites reached their infective stage, despite their increased crawling at that time, which is associated with mate searching. We did not find that trematodes reduced host survival, apart from expected increases in predation rate on amphipods; in fact, highly infected amphipods actually lived longer than lightly infected ones. Taken together, our results suggest that adaptive host responses can occur before parasite manipulation is realized