Demographic characteristics of young-of-year freshwater mussel populations in ponds
We describe demographics of young-ofyear (YOY) Pondmussels (Ligumia subrostrata) and Giant Floaters (Pyganodon grandis) in ponds during 2009 and 2011. YOY attained large size by approximately 6 months (Pondmussel, mean = 48.5 mm; Floater = 57.5), most individuals were sexually mature, and most females were gravid. Size and sex ratios varied among ponds. Pondmussel size was negatively related to mussel density, suggesting food competition; Floater size was not related to density. Size was not related to glochidial infestation pressure on fishes, suggesting that acquired immunity did not affect YOY performance. The percentage of gravid female Pondmussels varied between years from 27 to 100%, and 91% of female Floaters were gravid in 2011. Mean fecundity was high (Pondmussel = 34,311; Floater = 38,873). The proportion of gravid females and mean fecundity were not related to male density, showing that fertilization was efficient. Variation in size, sex ratios, and gravidity among ponds suggests that small differences in environmental conditions or demographic stochasticity can have large effects on populations. Rapid growth, early maturity, efficient fertilization, and high fecundity of YOY are contrary to traditional views of mussel life history, but these traits may allow Pondmussels and Floaters to rapidly colonize disturbed, unstable habitats.