Abstract
AbstractDensity‐dependent regulation is a fundamental part of ecological theory and a significant driver of animal demography often through complex feedback loops. We investigated the relationship between flood‐ and demographically induced fluctuations in density and the breeding propensity and survival of a pioneer species, the piping plover (plover, Charadrius melodus). We captured and marked adult and hatchling plovers on the Gavins Point Reach of the Missouri River in South Dakota and Nebraska, USA, from 2005 to 2014. In 2010 and 2011, historically high water levels and flooding inundated much of the plover's sandbar nesting habitat on the Missouri River. We developed a Bayesian formulation of a multievent model, or a multistate survival model with state uncertainty to estimate breeding propensity simultaneously with survival. Although plovers are conspicuous, their breeding status can be difficult to establish with certainty, which necessitated the use of uncertain states. With this model, we investigated the effect of sex, habitat availability, river flow, and density (birds/ha nesting habitat) on survival of hatch year and breeding and non‐breeding adult plovers. In addition, we estimated the transition rates for these age classes between breeding and non‐breeding states. Non‐breeding adults ( = 0.58 ± 0.06) had lower survival rates than breeding adults ( = 0.80 ± 0.04), and both breeding survival and breeding propensity decreased with increasing nesting density. Not only did survival and breeding propensity decrease directly at higher nest densities, but survival also was indirectly impacted by increasing the proportion of non‐breeding birds with relatively low survival. Thus, plovers were regulated through a complex set of feedback loops, acting as densities increased. Our findings underscore the intricacy of density‐dependent regulation and suggest that detailed demographic studies are needed to fully understand these effects.
Highlights
Population regulation through density dependence is a fundamental concept in ecology and underpins many of the fluctuations in animal abundance that we observe (Newton 1994, 1998)
Density-dependent population change often is a function of limited habitat negatively impacting one or more vital rate in a population, sometimes through complex negative feedback loops (Gill et al 2001)
Density can affect any of the demographic parameters that drive populations (e.g., Ferrer and Donazar 1996, Both 1998, Paradis et al 2002, Matthysen 2005), such that studies focused on understanding density-dependent population regulation should endeavor to look broadly to
Summary
Population regulation through density dependence is a fundamental concept in ecology and underpins many of the fluctuations in animal abundance that we observe (Newton 1994, 1998). Density-dependent population change often is a function of limited habitat negatively impacting one or more vital rate in a population, sometimes through complex negative feedback loops (Gill et al 2001). Piping plovers (Charadrius melodus, hereafter plovers) are migratory, territorial shorebirds that nest on sparsely vegetated beaches on the Atlantic coast, Great Lakes, and Great Plains in the United States and Canada (Elliot-Smith and Haig 2004). Across their range, disturbances (e.g., high-water events on rivers, reservoirs, and alkali lakes; coastal storms) are essential for maintaining early successional habitat. While significant gains have been made toward recovery (USFWS 2009), habitat limitation and resulting density-dependent regulation continue to plague the species
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