Skogen, Krissa .
Factors limiting reproductive output in declining populations of the rare New England perennial Desmodium cuspidatum (Fabaceae).
Plant conservation research has mostly focused on easily identified threats such as competition from invasive exotics, loss of genetic diversity, and habitat conversion, loss, or fragmentation. But some species decline even when their habitat seems largely intact. The perennial legume, Desmodium cuspidatum (large-bracted tick-trefoil, Fabaceae), has declined in New England, from 28 populations in 1976 to eight in 2004 though the habitat in which it is found seems largely unchanged. Because long-term persistence of populations requires recruitment of new individuals, identifying factors that limit reproductive success and seedling establishment are essential. Most individuals of D. cuspidatum do not reach their reproductive potential in New England populations. Hand pollination and bagging experiments in the field and greenhouse have shown that D. cuspidatum is self-compatible but seed set requires pollinators. Bagged but unmanipulated flowers fail to produce fruits. The average fruit: flower ratio is only about 0.05, and declines as flower number increases. The average seed: ovule ratio in mature fruit is approximately 0.80. Of seven extant populations monitored over 2 years, only four reported population increases. The only population found in habitat similar to that of historic records appeared to have higher survivorship (100%), recruitment rate (75%), and fruit: flower ratio (0.15) than populations found in habitats that do not resemble historic records (survivorship: 67-92%; recruitment: 30-50%; fruit: flower ratios: 0.006-0.10). In addition, fruit set almost completely failed in one of the two largest remaining populations, apparently due to weevil predation on flower buds. Fruit set and therefore recruitment in this species may be low due to pollinator limitation in populations found in habitats dissimilar from historic records, where pollinators are distracted from D. cuspidatum flowers by those of neighboring species with overlapping flowering periods not found in historic habitat.
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1 - University of Connecticut, Department of Ecology & Evolutionary Biology, 75 North Eagleville Rd. U-3043, Storrs, Connecticut, 06269-3043, USA
Presentation Type: Oral Paper
Location: Salon A - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 2:15 PM