| Chapter 1 explores temporal variation in a major environmental gradient in marine habitats, water flow, and how it interacts with species diversity of suspension feeding invertebrates to predict community-wide water filtration. I manipulated species diversity of suspension feeders and the presence of water flow directly in the lab and allowed communities to consume a diverse melange of phytoplankton. By tracking chlorophyll a concentrations over time, I was able to get a proxy for water filtration taking place at the community-level. Species diversity enhanced community filtration, and this response did not depend on whether water was flowing or not. However, individual species and pairs did respond to flow, so these results suggest that interactions between organisms and their modification of water flow may be important for predicting food delivery and ultimately water filtration over time. The balance of competition and niche complementarity appeared to change across flow regimes, which brings species interactions, and their sensitivity to environmental conditions, to the forefront.;Chapter 2 investigates a common form of spatial heterogeneity on a rocky shore, namely topography generated by space-holding barnacles and how it interacts with grazer species diversity to drive algal community succession. This chapter was part of a project started by Kristin Aquilino in which we simultaneously manipulated barnacle cover and snail grazer diversity at small scales relevant to seaweed-grazer interactions. Then we tracked communities over time as they recovered from algal clearing. The presence and heterogeneity of barnacles along with the diversity and identity of grazing invertebrates interacted to predict algal succession. Grazer diversity itself was important for suppressing early successional microalgae, while later successional macroalgae were promoted by the presence of a key limpet grazer. In the absence of this limpet heterogeneity in barnacle cover led to increased algal accumulation. Again, species interactions and the potential for niche complementarity depended on habitat heterogeneity, thus the influence of environment on interactions remains strong thread in the dissertation.;Chapter 3 also considers topographic heterogeneity on rocky shores, but this time focusing on how topography at different spatial scales modifies community structure during early succession. We have known for a long time that large elevation gradients on rocky shores are critical for the distributions of organisms, but perhaps small scale environmental variation also matters for these communities as suggested by many previous studies. I decided to manipulate small-scale (mm) topography by making settlement plates that mimicked real rock surfaces. Then I placed these plates across areas of mid-intertidal a rocky shore, which represented larger scale (cm to m) variation in topography, including differences in elevation and distance to shore. Importantly, both scales of environmental heterogeneity influenced community composition, but in different ways. Early successional algae responded more strongly to the large-scale heterogeneity present along and across the coastline, while mobile invertebrates responded strongly to small-scale characteristics like rugosity and convexity. It is likely then that small-scale heterogeneity can have a driving influence on algal distributions indirectly through the grazing behaviors of invertebrate animals, but once again this will depend on the traits of the grazers (e.g., body size) and how they interact with heterogeneity.;One conceptual result that helps tie all of these chapters together is that in order for environmental heterogeneity to be important to ecological communities, the scale at which heterogeneity occurs must match response and effect traits of the organisms living within the community. Body size and the way organisms of a particular size respond to, and potentially modify, their abiotic surroundings play a role in every chapter, from the fouling invertebrates that emerge from the substrate into flowing water (Chapter 1) to the tidepool invertebrates that crawl on bumpy substrates in search of food and refuge (Chapters 2, 3). All of this work, I hope, will help advance ecological knowledge and our collective ability to make predictions in a changing world. Yet, it is likely that the work presented here will generate more questions than answers. (Abstract shortened by ProQuest.). |
