Effect of habitat area and fragmentation on tropical seawall biodiversity: A landscape scale experimental study

Habitat loss and fragmentation is one of the largest areas of study in ecology and conservation biology and the use of species-area relationship (SAR) models to predict species extinctions and community changes are fundamental... [ view full abstract ]

Habitat loss and fragmentation is one of the largest areas of study in ecology and conservation biology and the use of species-area relationship (SAR) models to predict species extinctions and community changes are fundamental to this field. However, empirical work has lagged behind the many theoretical advances as isolating the effects of habitat fragmentation experimentally is considered especially difficult. This is because the level of fragmentation often co-varies with habitat area and hence their effects can easily be confounded. In our study, we addressed this issue by using moulded concrete tiles to create standard units of ‘habitat patches’ and arranged them in nine different, fully replicated, plot configurations on seawalls in Singapore. By doing so, we were able to test both the independent and interactive effects of habitat area and fragmentation on the diversity of the macroscopic intertidal community. We adapted the countryside SAR model to incorporate the roles of both matrix and fragmentation pattern to test our hypotheses and explored the mechanisms underlying our results. To our knowledge, no previous manipulative experiment has simultaneously manipulated both these factors independently in a marine ecosystem. We found a unimodal relationship between species richness and habitat fragmentation and postulate that a combination of high-level processes can give rise to this observed pattern. We discuss how these results can help inform efforts to ecologically engineer coastal defences worldwide.