Spatial patterns reveal negative density dependence and habitat associations in tropical trees

Abstract

Abstract. Understanding how plant species coexist in tropical rainforests is one of the biggest challenges in community ecology. One prominent hypothesis suggests that rare species are at an advantage because trees have lower survival in areas of high conspecific density due to increased attack by natural enemies, a process known as negative density dependence (NDD). A consensus is emerging that NDD is important for plant-species coexistence in tropical forests. Most evidence comes from short-term studies, but testing the prediction that NDD decreases the spatial aggregation of tree populations provides a long-term perspective. While spatial distributions have provided only weak evidence for NDD so far, the opposing effects of environmental heterogeneity might have confounded previous analyses. Here we use a novel statistical technique to control for environmental heterogeneity while testing whether spatial aggregation decreases with tree size in four tropical forests. We provide evidence for NDD in 22% of the 139 tree species analyzed and show that environmental heterogeneity can obscure the spatial signal of NDD. Environmental heterogeneity contributed to aggregation in 84% of species. We conclude that both biotic interactions and environmental heterogeneity play crucial roles in shaping tree dynamics in tropical forests.

Spatial Cluster and Outlier Identification of Geochemical Association of Elements: A Case Study in Juirui Copper Mining Area

“…They are aggregated in patches or formed gradients or other kinds of spatial patterns (Legendre and Fortin, 1989). Spatial patterns have been widely used in different research fields such as biometrics (Fuentes et al, 2006), landscape ecology (Bagchi et al, 2011;Irl et al, 2015), regional economics (Monastiriotis, 2009) and medicine (Waller and Gotway, 2004;McLaughlin and Boscoe, 2007;Goovaerts and Jacquez, 2004) etc. Extraction of spatial information for mineral exploration can be achieved through the study of spatial distribution patterns of regional geochemical elements such as spatial structures, spatial variability and spatial association patterns (spatial clustering and spatial outliers).…”

Relaxation of species‐specific neighborhood effects in Bornean rain forest under climatic perturbation

“…In the temperate relatively species-poor forests, there is more evidence for NDD operating on small trees as a result of competition from larger conspecific ones (Canham et al 2004(Canham et al , 2006. In the tropical forests after thinning among the seedlings, and perhaps smaller saplings, conspecific trees are often not close enough to compete directly, unless they are strongly clustered as a result of limited dispersal (Condit et al 2000, Seidler andPlotkin 2006) or edaphic factors selecting their local distributions (Ashton 1998, Bagchi et al 2011. In some cases, positive density dependence (PDD) may be operating, whereby seedlings, saplings, and smaller trees are facilitated in their growth and clustering is thereby strengthened.…”

Estructura espacial y dinámica del bosque montano del sur del Ecuador. Interacciones bióticas y limitaciones abióticas

“…Furthermore, trunk height is frequently used as a proxy for age in tree ferns (Seiler 1981, Bittner and Breckle 1995, Seiler 1995. Individual tree ferns were classified according to the 99th percentile (h99) of the distribution of individual heights (Bagchi et al 2011). Tree ferns with a height > h99 x 2/3 were classified as adults, while trees with a height < h99 x 1/3 were classified as juveniles (Fig.…”

“…Trees with a height between 1/3 and 2/3 of the 99th percentile were excluded from the cohort analyses. Although these classes would probably not agree with a strict demographic classification of adults and juveniles, we used these terms following recent studies on NND in tropical forest (Bagchi et al 2011) and for the sake of brevity.…”

“…However, few attempts have been made to explicitly test the effects of specific environmental factors (but see Bagchi et al 2011) With this in mind, we fully mapped three plots representing contrasting succession stages in an evergreen tropical montane forest in southern Ecuador. We conducted parallel analyses in successional stages as plant-plant interactions and ontogenetic necessities shift abruptly along succession in tropical forests (Franklin and Rey 2007 (Arens 2001).…”