Title
Defaunation increases the spatial clustering of lowland Western Amazonian tree communities
Date Issued
01 July 2018
Access level
open access
Resource Type
journal article
Author(s)
Bagchi R.
Swamy V.
Latorre Farfan J.P.
Terborgh J.
Vela C.I.A.
Pitman N.C.A.
Publisher(s)
Blackwell Publishing Ltd
Abstract
Declines of large vertebrates in tropical forests may reduce dispersal of tree species that rely on them, and the resulting undispersed seedlings might suffer increased distance- and density-dependent mortality. Consequently, extirpation of large vertebrates may alter the composition and spatial structure of plant communities and impair ecosystem functions like carbon storage. We analysed spatial patterns of tree recruitment within six forest plots along a defaunation gradient in western Amazonia. We divided recruits into two size cohorts (“saplings”: ≥1 m tall and <1 cm diameter at breast height [dbh], and juveniles, 1–2 cm dbh) and examined the spatial organisation of conspecific recruits within each cohort (within-cohort) and around conspecific reproductive-sized trees (between-cohort). We used replicated spatial point pattern analysis to quantify relationships between recruit clustering and cohort, defaunation intensity, each tree species reliance on hunted dispersers and the interactions among these three covariates. Within-cohort clustering of conspecific saplings increased with reliance of tree species on hunted dispersers, and this trend strengthened significantly as defaunation increased, probably because of reduced dispersal. Within-cohort clustering of conspecifics declined from saplings to juveniles, suggesting density-dependent mortality of saplings. However, the positive relationship between sapling clustering and defaunation did not lead to greater reductions in within-cohort clustering during the sapling–juvenile transition, suggesting that higher conspecific densities did not translate into increased mortality. Instead, the increased spatial clustering associated with defaunation was retained for juvenile recruits. Between-cohort clustering was unrelated to defaunation and did not change during the sapling–juvenile transition. Synthesis. Defaunation increased spatial aggregation of saplings of tree species reliant on hunted dispersers. The increase in sapling clustering did not increase density-dependent thinning, and persisted into older recruit cohorts, suggesting that hunting may initiate long-term spatial reorganisation of Amazonian tree communities. The lack of increased density-dependent thinning indicates that reduced dispersal did not increase mortality of large-vertebrate dispersed tree species that contribute disproportionately to forest biomass. We, therefore, caution against the fait accompli acceptance of the prediction by recent modelling studies that overhunting will precipitate a collapse in carbon sequestration by tropical forests.
Start page
1470
End page
1482
Volume
106
Issue
4
Language
English
OCDE Knowledge area
Ecología
Subjects
Scopus EID
2-s2.0-85042131865
Source
Journal of Ecology
ISSN of the container
00220477
Sponsor(s)
Financial support for field data collection was provided by the National Science Foundation, USA (DEB 0742830), Andrew Mellon Foundation, Wildlife Conservation Society Research Fellowship Program, Amazon Conservation Association Seed Grant, Conservation, Food and Health Foundation and the National Geographic Society Committee for Research and Exploration (9487-14). Logistic support for fieldwork was provided by Cocha Cashu Biological Station (CC sites), Rainforest Expeditions (TRC site), Inkaterra Association (RA site), and Centro de Investigación y Capacitación Río Los Amigos (LA site). Research authorisation for field data collection was granted by Peruvian government agencies Servicio Nacional de Areas Naturales Protegidos por el Estado—SERNANP (CC and TRC sites) and Servicio Nacional Forestal y de Fauna Silvestre—SERFOR (LA and RA sites). V.S. was supported by a Charles Bullard Fellowship in Forest Research from Harvard University (2012-13). R.B. was supported by a fellowship from the European Union's Seventh Framework Program for Research, Technological Development and Demonstration under grant agreement no. GA-2010-267243—PLANT FELLOWS.
Sources of information:
Directorio de Producción Científica
Scopus