Neighbour‐regulated mortality: the influence of positive and negative density dependence on tree populations in species‐rich tropical forests

Abstract

Density-dependent mortality has long been posited as a possible mechanism for the regulation of tropical forest tree density. Despite numerous experimental and phenomenological investigations, the extent to which such mechanisms operate in tropical forests remains unresolved because the demographical signature of density dependence has rarely been found in extensive investigations of established trees. This study used an individual-based demographical approach to investigate the role of conspecific and heterospecific neighbourhood crowding on tree mortality in a Panamanian and a Malayan tropical forest. More than 80% of the species investigated at each site were found to exhibit density-dependent mortality. Furthermore, most of these species showed patterns of mortality consistent with the Janzen-Connell hypothesis and the rarely explored hypothesis of species herd protection. This study presents some of the first evidence of species herd protection operating in tree communities.

Forest tree neighborhoods are structured more by negative conspecific density dependence than by interactions among closely related species

“…However, most other studies of seedling and sapling growth and survival in forests have similarly detected density-dependent effects at scales < 30 m (Curran and Webb 2000, Hubbell et al 2001, Peters 2003, Uriarte et al 2004b, Comita and Hubbell 2009). …”

Loss of animal seed dispersal increases extinction risk in a tropical tree species due to pervasive negative density dependence across life stages

“…Most empirical research on NDD in tree species has focused on seeds [18] and seedlings [22], although several studies have also detected NDD for later life stages, including saplings [19,23] and adult trees [24]. Few studies have integrated effects of NDD across life stages [25,26], and no studies, to our knowledge, have directly quantified the effects of NDD across all tree life stages, from seeds to adults.…”

Density dependence on tree survival in an old-growth temperate forest in northeastern China

“…Neighborhood processes can influence survival, recruitment, and growth of plant species positively through facilitation (Wills et al, 1997) or negatively by competition (Getzin et al, 2006;Gratzer and Rai, 2004), and indirectly by specialist herbivores and pathogens (Dobbertin et al, 2001;Gunton and Kunin, 2007;Hyatt et al, 2003;Janzen, 1970;Peters, 2003). These processes together to regulate species coexistence (Pacala, 1989;Peters, 2003;Volkov et al, 2005;Wills et al, 2006).…”

“…Field studies have demonstrated density dependence of varying extents in different species (e.g., He and Duncan, 2000;Hubbell and Foster, 1986;Kenkel, 1988;Peters, 2003;Wills and Condit, 1999;Wills et al, 1997). However, it is still unclear to what degree and spatial scale that density-dependent interactions among species may play a role in plant populations, especially in diverse, mixed tree communities (Gunton and Kunin, 2007;John et al, 2002).…”