Moving from pattern to process: coexistence mechanisms under intermediate disturbance regimes

Abstract

Coexistence mechanisms that require environmental variation to operate contribute importantly to the maintenance of biodiversity. One famous hypothesis of diversity maintenance under disturbance is the intermediate disturbance hypothesis (IDH). The IDH proposes patterns of peaked diversity under intermediate disturbance regimes, based on a tension between competitively superior species and species which can rapidly colonize following disturbance. We review the literature, and describe recent research that suggests that more than one underlying mechanism can generate this unimodal diversity pattern in disturbed environments. Several exciting emerging research areas are identified, including interactions between disturbance types, operation of the IDH in multi-trophic systems, and changes in disturbance regimes. However, empirical work is still focussed on describing the IDH pattern, with little emphasis on identifying its mechanistic basis. We discuss how to extend methods for identifying different coexistence mechanisms, developed in the theoretical literature, to experimental research. In an attempt to operationalize these various ideas we outline a hypothetical IDH research programme. A solid understanding of the life history attributes of the component species and their responses to disturbance will facilitate identification of the coexistence mechanism(s) underlying the IDH pattern, and provide a framework by which empirical and theoretical results can be more fully integrated.

Contrasting taxonomic and functional responses of a tropical tree community to selective logging

“…in composition among stems that will live to reproduce and contribute to subsequent generations (Shea, Roxburgh & Rauschert 2004;Haddad et al 2008). Indeed several tests of the intermediate disturbance hypothesis in tropical trees (e.g.…”

“…Indeed, in some communities where disturbance reduces or has no effect on diversity at small spatial scales, diversity at larger spatial scales is actually enhanced because a matrix of sites favouring species with complementary ecological requirements is created (Cadotte 2007;Berry et al 2008). The pertinent scale of this effect is likely determined by the dispersal abilities of the study organism (Shea, Roxburgh & Rauschert 2004;Haddad et al 2008), and for trees we expect infrequent colonization events beyond several hundred metres up to several kilometres (Nathan & Muller-Landau 2000;Sheil & Burslem 2003). Therefore, it is important to consider the spatial distribution of gaps in the studied forest, especially when assessing appropriate interventions for forest management.…”

Composition of woody species in a dynamic forest-woodland-savannah mosaic in Uganda: implications for conservation and management

“…And the highest number of species can only be conserved when complementary areas are included in the conservation plan (Howard et al 1998). The maintenance of the high diversity of Budongo, being an isolated forest with no immediate source of additional forest species, may be more attributed to the existence of all stages of the succession gradient (Richardson-Kageler 2004;Shea et al 2004) than acquisition of more forest species from elsewhere, which, additionally, often takes a long time (Chapman et al 1997). Hence, if reforestation of Budongo Forest Reserve would continue to the extent that the woodland areas would be lost, the biodiversity of the reserve would probably decrease.…”

“…For purposes of conserving woody plants in a dynamic landscape, it is thus important that each vegetation type represented is included and maintained within the conservation area (Bengtsson et al 2003). In the area under study, fire disturbance is a requirement for species coexistence (Shea et al 2004).…”

Effects of regular and irregular temporal patterns of disturbance on biomass accrual and species composition of a subtidal hard-bottom assemblage

“…Common to the diVerent kinds of disturbance is the release of limiting resources, e.g. substrate, which alters niche opportunities (Shea et al 2004). Previous studies on disturbance-diversity relationships did not allow for drawing general conclusions on the eVects of disturbance.…”