Sabrina E. Russo
Date of this Version
Huanca-Nunez (2017) Variation in Density Dependent Seedling Survival across Forests of Different Successional Age and Hunting Protection Status. MS Thesis, University of Nebraska-Lincoln
Over 50% of the original extent of tropical forests has been cleared. Restoration of secondary forests is important for maintaining the ecosystem services that mature tropical forests provide. Density dependence (DD) is thought to be a major mechanism for shaping forest community structure and may cause reduced spatial aggregation among individuals of the same species, allowing for maintenance of diversity. While much research has focused on DD in mature tropical forests, few studies have examined how DD may influence community structure in secondary forests, many of which are also exposed to hunting. There are several important agents of negative and positive DD, including natural enemies and mutualists of trees. Mammals are important herbivores of seedlings. Hence, forest protection status is also likely to be a key factor influencing density-dependent seedling survival because it affects populations of mammals through trophic cascades. Here, we address the questions, (1) Is there an overall density dependent effect? (2) How the type, direction, and strength of DD differ between forests of different successional ages and protection status? We used neighborhood models fit to one-year survival of 8,042 seedlings of 114 species in early successional to old growth plots with different protection status in northeastern Costa Rica. We found that, averaging across forests, there was a negative significant conspecific density dependent effect (CND). Despite this overall effect, there was also significant variation among forests of different successional age and protection status. CND strength increased with successional age in protected forest and decreased in unprotected forests.
Adviser: Sabrina E. Russo