Habitat structure mediates biodiversity effects on ecosystem properties

Abstract

Much of what we know about the role of biodiversity in mediating ecosystem processes and function stems from manipulative experiments, which have largely been performed in isolated, homogeneous environments that do not incorporate habitat structure or allow natural community dynamics to develop. Here, we use a range of habitat configurations in a model marine benthic system to investigate the effects of species composition, resource heterogeneity and patch connectivity on ecosystem properties at both the patch (bioturbation intensity) and multi-patch (nutrient concentration) scale. We show that allowing fauna to move and preferentially select patches alters local species composition and density distributions, which has negative effects on ecosystem processes (bioturbation intensity) at the patch scale, but overall positive effects on ecosystem functioning (nutrient concentration) at the multi-patch scale. Our findings provide important evidence that community dynamics alter in response to localized resource heterogeneity and that these small-scale variations in habitat structure influence species contributions to ecosystem properties at larger scales. We conclude that habitat complexity forms an important buffer against disturbance and that contemporary estimates of the level of biodiversity required for maintaining future multi-functional systems may need to be revised.

Figure 1.

Model visualization of the effects of the four-way interaction heterogeneity × species composition × connectivity × location on invertebrate net movement (Δbiomass g⁻¹) between patches. Horizontal bars represent the predicted values from the minimal adequate regression model in (a) H_A and connectivity 50%, (b) H_A and connectivity 100%, (c) H_B and connectivity 50%, and (d) H_B and connectivity 100%. Abbreviations for species composition: CV, C. volutator; HU, H. ulvae; HD, H. diversicolor. The species mixture is represented by the grey horizontal bars. Locations 1, 3, 5 and 7 represent the patches and locations 2, 4 and 6 represent the corridors. Individual data points are not shown, because the GLS analysis allows for differences in spread for location and habitat heterogeneity.

Figure 2.

Model visualization of the effects of the two-way interaction: (a) species composition × connectivity and the single term; (b) location on bioturbation intensity at the patch scale. Horizontal bars represent model predictions from the minimal adequate regression model. Species identities: 0, no macrofauna; CV, C. volutator; HU, H. ulvae; HD, H. diversicolor. The species mixture is represented by the grey horizontal bars. Individual data points are not shown because the GLS analysis allows for differences in spread for species composition, patch connectivity and location. Raw data boxplots are presented in electronic supplementary material, figure S3.

Figure 3.

Model visualization of the predicted effects of (a) species composition and (b) patch connectivity (%) on NH₄-N concentration (mg l⁻¹). Individual data points are omitted, because the GLS analysis allows for different spread in species composition. Species identities: 0, no macrofauna; CV, C. volutator; HU, H. ulvae; HD, H. diversicolor. Raw data boxplots are presented in electronic supplementary material, figure S4.

Figure 4.

Model visualization of the predicted effects of (a) species composition, (b) patch connectivity (%) and (c) heterogeneity on PO₄-P concentration (mg l⁻¹). Individual data points are omitted, because the GLS analysis allows for different spread in species composition. Species identities: 0, no macrofauna; CV, C. volutator; HU, H. ulvae; HD, H. diversicolor. Raw data boxplots are presented in electronic supplementary material, figure S5.