Gap percolation in rainforests

Abstract

Rainforests biodiversity is sustained by the three-dimensional structure of their canopy which provides a wide range of physical microenvironments. Given the dynamic nature of the forest, the recognition of stable vertical layers or strata in the canopy is controversial. The spatial characterisation of potential habitats of understory species is not straightforward due to the complex structure of rainforest canopies and the wide ecological variability to which rainforest species can be adapted. Here we present a new description of potential understory habitats that give rise to a well-defined characteristic vertical scale of forest organization h c :/13 m. Species living in microenvironments occurring at canopy heights below this critical height h c can only experience landscapes with disconnected habitat patches (i.e. fragmented habitat landscapes), while those species capable of living also above h c will experience a fully connected landscape of suitable microenvironmental conditions. The possible implications for plant dispersal and animal colonisation strategies living at the understory or close-to-floor are discussed in relation to rainforest gap-dynamics, habitat loss and habitat fragmentation processes. Longrange and directed dispersal strategies (e.g. plant seed dispersal by animals) are optimal for those species living below h c , providing the best exploration of scarce habitats and a major robustness to habitat changes. On the other hand, dispersal strategies of those species capable to exploit habitats above h c need not to be based on directed long-range mechanisms. Different dispersal strategies may in turn imply different sensitiveness of species to habitat loss and habitat fragmentation processes in the rainforest.

Transition from Connected to Fragmented Vegetation across an Environmental Gradient: Scaling Laws in Ecotone Geometry

“…The significance of percolation theory for ecology was recognized in the late 1980s (Gardner et al 1987). Since then, a number of papers have investigated habitat maps with simulations and field data (Gustafson and Parker 1992;Milne 1992;Loehle et al 1996;Li 2002;He and Hubbell 2003;Solé et al 2005). Effects of percolation on population dynamics have also been investigated (Andrén 1994;With and Crist 1995;Bascompte and Solé 1996;Oborny et al 2007).…”

“…Gap structure was studied with a uniform percolation model in a rainforest in Panama (Solé et al 2005). Complementary information (about gap structure and patch structure) would be important in a variety of landscapes, because in an autocorrelated case (e.g., in a UCP or a GCP), the statistics of occupied patches cannot be expected to be the same as the statistics of the vacant patches (unlike those in a URM or a GRM).…”

The disentangled bank: How loss of habitat fragments and disassembles ecological networks

“…Network approaches ( Bascompte, 2007 ) to biodiversity science have improved our understanding of the causes and consequences of biodiversity loss ( Sol é et al, 2005 ;Tylianakis et al, 2008 ). Network-based representations of ecological systems are powerful models that can describe biodiversity change ( McCann, 2007 ) and characterize structural (e.g., Rayfi eld et al, in press) and functional consequences of fragmentation ( Stouffer and Bascompte, 2010 ).…”

A Pair-Approximation Model for Spatial Patterns in Tree Populations with Asymmetrical Resource Competition

“…Manrubia and Solé (1997) and Pagnutti et al (2005) dealt with lattice models of forest dynamics with a richer vertical layering; Solé et al (2005) addressed the interaction between dispersal strategies and vertical forest stratification. These authors used simulations of cellular automata.…”