The Maintenance Of Biological Diversity In Heterogeneous Environments

Author : Matthew Adam Whalen
Publisher :
ISBN 13 : 9780355450941
Total Pages : pages
Book Rating : 4.4/5 (59 download)

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Download or read book The Role of Environmental Heterogeneity in Shaping Biodiversity-ecosystem Function Relationships written by Matthew Adam Whalen and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: From global-scale variation in the distribution of light reaching the Earth’s surface to the smallest chemical gradients, environmental heterogeneity, or variation in environmental conditions over space and time, is critical to explain process and pattern in nature. Environmental heterogeneity has long been hypothesized to promote species coexistence by allowing niche partitioning. Organisms respond to heterogeneity in abiotic environmental conditions at several scales, interactions between organisms can be mediated by heterogeneity, and organisms themselves can generate additional heterogeneity that may be important for the structure of communities. Importantly, how environmental heterogeneity interacts with biodiversity remains an important challenge to predicting the ecosystem functioning. Moreover, given that environmental conditions and ecological process change across scales of space and time, investigating how heterogeneity influences ecological communities – both directly by modifying habitat quality and indirectly by modifying interactions – across a range of scales is necessary if we want to make predictions in community ecology. Ecologists often observe and measure communities at a single scale, which often not the scale at which processes take place, so defining appropriate scales for inquiry can be challenging. If a single scale is chosen, ecologists must consider the natural history of their systems that relate to the patterns and processes being investigated. However, the ability of ecologists to view systems at several scales at once is improving with technological advances. My goal with this dissertation was to take what we already know about biodiversity maintenance and ecosystem functioning and extend it to multiple trophic levels, habitats, and scales of observation, all of which are important to our general understanding of community ecology. The real world is messy, which makes the job of a community ecologist simultaneous fascinating and frustrating. However, by considering some of the complexities inherent in natural systems (including how they might change across scale) I aim to help in pushing biodiversity science into the 21st Century. All of the following chapters explore some aspect of environmental heterogeneity and how it either influences biodiversity or interacts with it to determine some important ecological process. 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 mélange 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. For instance, how do we take the ideas laid out in this dissertation and marry them with life histories, which often cause organisms to experience very different scales of environmental heterogeneity over their lifetimes? If we want to make large-scale predictions about the abundance and distribution of life on Earth and how it responds to environmental change, how much information do we actually need to know at the small scales? Give that body size is important for metabolic rates and impacts on ecosystems, might there be ways to combine scaling and metabolic theories in ecology, which strive for simplicity, with the messier information about environmental heterogeneity and species traits to make predictions across different types of ecosystems? These are the types of questions that continue to motivate me and that, hopefully, motivates the field of ecology in the future.