Biological Dynamics of Forest Fragments Project - Project Development and Hypothesis

Project Development and Hypothesis

The study of habitat fragmentation found its roots early, with Aldo Leopold’s ideas on “edge effect” and Alfred Russel Wallace’s and E. O. Wilson’s studies and models of island biogeography laying a foundation for the field (Laurance and Bierregaard 1997). These concepts offer potential applicable and hypothetico-deductive value for the study of forest fragmentation and have inspired debates about habitat reserve design.

Generally speaking, the theory of island biogeography represents a collection of interwoven ideas (Harris 1984), describing patterns of floral and faunal communities on marine islands. It models fundamental processes such as dispersal, diversity and population dynamics of islands with regards to their area and distance from other islands or the mainland. Theoretically, forest fragments take on the characteristics of habitat islands in proportion to their degree of and length of time of isolation (Harris 1984). Island biogeography theory and lessons learned from true-island biogeography provide a basis for developing a management strategy and addressing specific decision variables, such as reserve patch size, distribution, placement and protective measures (Harris 1984). Nevertheless a notable difference between oceanic islands and terrestrial islands, or fragments, is the existence of land surrounding or between the fragments, referred to as the matrix. The impacts of use and management of this space is a continued subject of study.

Observations of edge effects on habitats are also important, if not integral, to the study of fragmentation effects. A slew of changes in habitat and trophic interactions have been observed to magnify as distance from habitat edge decreases, such as nest predation, decreased humidity and soil moisture, sunlight, decreased species richness and changes in species constitution. The degree of these impacts on fragments continues to be studied. Due to the generally high ratio of edge to habitat area in fragments, edges are presumed to have detrimental consequences for the organisms that inhabit forest fragments.

These concepts have largely inspired the SLOSS (single large or several small) reserve size debate, which the Minimal Critical Size of Ecosystem Project (now known as the BDFFP) attempts to address. The SLOSS debate is an ongoing interdisciplinary discussion in which the scientific community attempts to understand and weigh the pros and cons of different reserve size and distribution, for successful ecosystem conservation: single large reserve, or several small ones? Increasing and widespread habitat loss and fragmentation, along with the SLOSS debate, have led to the questions the BDFFP originally sought to answer. Overall, Lovejoy’s goal in establishing the project was to determine necessary reserve size and placement for successful habitat and species conservation, hence the original name of the project. According to Bierregaard's book, Lessons from Amazonia, Lovejoy worked off of the Island Biogeography Theory and asked three key questions:

1) What effect does fragment size have on the rate of species extinction? 2) Would the local extinction rate eventually slow and halt, equalizing the number of species? 3) How do species interactions and demography change as a result of reduced habitat?

Since then, studies conducted on the BDFFP site have varied enormously in terms of their principal goals and hypotheses (Laurance and Bierregaard 1997). Along with reserve size, placement and distribution, it also important to understand and properly manage the links between habitat fragmentation and ecosystem persistence (Bierregaard 2001). Studies on edge effects, extinction rates, biotic and abiotic interactions, mortality factors, soil quality and more performed on this site address fragmentation effects on biodiversity and other ecological changes. Other dimensions influencing ecosystems are also studied, such as economic and human factors. Many studies in BDFFP also attempt to find ways to apply research to restoration, conservation and management practices of tropical forests. The original core question of minimum ecosystem reserve size has initiated an incredible variety of research that continues to grow and diversify.