title: Effects of habitat degradation, microsite, and seed density on the persistence of two native herbs in a subtropical shrubland.
abstract: OBJECTIVE
  Species in degraded ecosystems may interact differently with their surroundings from those under historic conditions. Understanding factors affecting variation in early life history stages of plants is fundamental to assessing their persistence in intact and degraded habitats, and the value of degraded lands. We evaluated the effect of seed density on the seed dynamics of two herbaceous species (annual, biennial), and considered how seed availability may influence population dynamics in different habitats (degraded, intact Florida scrub) and microsites (bare sand, leaf litter, shrub).
  
  
  METHODS
  We used data on responses to experimental treatments (seed removal, seedling emergence, establishment) and models to evaluate how effects of these factors may change over time since the last disturbance.
  
  
  RESULTS
  Probability of any seed removal, emergence, and establishment per unit increased with seed density, although proportion removal for Chamaecrista fasciculata, proportion emergence for Balduina angustifolia, and proportion establishment for both species decreased with density. When animals were given selective access to seeds, invertebrates were primarily responsible for seed removal of both study species. Models with dynamics changing with time-since-disturbance for both species predicted that population growth may decrease slightly if local available seed density increases.
  
  
  CONCLUSIONS
  Detailed demographic comparisons of populations in intact and degraded conditions can be used to understand the way that environmental conditions (habitat, microsite) combine with seed density effects to influence population dynamics of herb species. Degraded habitat may act as a transitional state in a trajectory toward intact conditions for some species, or as refugia for other native species.
authors.affiliation: Department of Biology, University of Central Florida, Orlando, Florida 32816-2368 USA estephens@knights.ucf.edu.
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Stephens
authors.affiliation: Department of Biology, University of Central Florida, Orlando, Florida 32816-2368 USA.
authors.forename: Pedro F
authors.initials: PF
authors.lastname: Quintana-Ascencio
mesh_terms: D019659:Asteraceae / Q000502:physiology*; D003247:Conservation of Natural Resources; D017753:Ecosystem; D007887:Fabaceae / Q000502:physiology*; D005431:Florida; D011156:Population Density; D011157:Population Dynamics; D012639:Seeds / Q000502:physiology
keywords: Florida; anthropogenic disturbance; plant populations; population dynamics; restoration