Describing Species-environment Relations for Macrobenthic and Microphytobenthic Community Structure Using Constrained Ordination and Predicting Environmental Variables from Species Composition PDF Download

Author: Angeliki Evgenidou
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Category : Species diversity
Languages : en
Pages : 862

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Author: Allison K. Barner
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ISBN:
Category : Bioclimatology
Languages : en
Pages : 268

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Ecologists must increasingly balance the need for accurate predictions about how ecosystems will be affected by climate change, against the fact that making such predictions at the ecosystem-level may be infeasible. Although information about responses of individual species to a changing environment is increasing, scaling such information to the community level is challenging. To date, predicting responses of ecological communities to climate change is constrained by limited theoretical and empirical knowledge about the response of communities and ecosystems to change. My dissertation addresses several knowledge gaps in our understanding of community structure under climate change. This research draws from a rich experimental tradition in the species-diverse model ecosystem of the US Pacific Northwest rocky intertidal to test ecological theory. In Chapter 2, I assessed whether the response of multiple species of coralline algae to global change could be predicted from basic first principles of chemistry, physiology, and ecology. Given the rate of global change, and the time-consuming process of experimentally determining species responses to climate change, I hypothesized that species can be grouped using existing theory, either by their evolutionary relatedness or by their ecological traits, such that climate responses are similar within a group. Such a scheme would greatly reduce the number of experiments needed to characterize species climate vulnerability, requiring the characterization of the response of groups of species to climate change, rather than individual species. Using a suite of five co-occurring species of intertidal articulated coralline algae (Corallina vancouveriensis, Corallina officinalis, Bossiella plumosa, Bossiella orbiginiana, and Calliarthron tuberculosum), I applied this framework to generate ten mutually exclusive hypotheses that could explain organismal response to ocean acidification, a consequence of global climate change that threatens marine calcifying species. I found that all species had similar responses to ocean acidification, and that responses were generally predicted by the body size of the individual. Despite the power that such a framework provides in understanding group-level response to climate change, predicting community-level response requires knowledge of how organisms affect one another. In Chapter 3, I quantified species interactions in a series of removal experiments to estimate the reciprocal effects between a canopy-forming intertidal kelp (Saccharina sessilis) and a suite of understory species that persist beneath the kelp canopy. This experiment was replicated in different oceanographic conditions across a large latitudinal gradient, as a step towards understanding how interactions might change with climate change. However, the experiment demonstrated that interactions between the canopy and understory were consistent among different environmental conditions. Furthermore, the strongest effect was that of understory species, particularly articulated coralline turf algae, on the canopy species. The coralline turf algae both facilitated the recruitment of the canopy species and buffered the canopy from abiotic stress during its adult life stage. Combining experimental results and observational surveys, a hypothesized interaction network for these species was constructed, highlighting the importance of direct and indirect species interactions in promoting species coexistence. A long-standing controversy in ecology is whether or not species interactions can be inferred from observational data, as opposed to from experimental tests. Although the rocky intertidal ecosystem is unique for its ease of experimental manipulation, quantifying species interactions experimentally is often difficult or impossible. As an alternative, many have turned to statistical methods to estimate species interactions from observational data, namely, from patterns in species pairwise co-occurrences. In Chapter 4, I examined these co-occurrence methods and their potential relationship to experimentally measured species interactions. I first used a suite of different co-occurrence methods to generate a set of predicted species interactions of macrophytes and invertebrates from observational surveys conducted in the rocky intertidal zone of Oregon. I then compared the predicted species interactions to the same pairwise species interactions determined experimentally and assembled from the literature. Overall, of the seven methods tested, each generated a different set of predicted species interactions from the same data, and all methods predicted interactions that did not match those in the experimental database. Thus, predicting species interactions from patterns in occurrence remains elusive. Importantly, much work remains to be done to understand the link between species co-occurrences and their actual interactions with one another on the landscape. A key limiting frontier in climate change ecology is determining the influence of species interactions on species distributions across the landscape, and the sensitivity of such interactions to changes in climate. Finally, in Chapter 5, I used theory from the published literature and knowledge from my previous chapters to make predictions the recovery of low rocky intertidal communities after a disturbance. The process of community development after disturbance has been studied in many ways, from the successional studies of the early 1900s, to modern community assembly theory. In recent years, a focus on the unpredictability of community assembly has emerged, paying particular attention to the role of historical contingency, or priority effects, in determining the recovery trajectory of a community. Priority effects occur when the arrival of a species after a disturbance inalterably changes the composition of the developing community, driving the assembly of widely different communities at a small spatial scale. I conducted a community assembly experiment in three different low intertidal zone community "types", each characterized by different dominant macrophyte species (Saccharina sessilis, Phyllospadix spp., and algal "turfs"). Replicating this experiment at six sites along the Oregon coast, I found that both regional and local dynamics constrain the recovery of communities after disturbance. Half of the time, the community returned to the state of the nearby community type. The remaining communities were influenced by priority effects that could be predicted based on 1) regional dynamics favoring some species over others, or 2) the timing of arrival of important facilitating species. Overall, understanding the dynamic relationship between the persistence of diverse communities and a changing environment remains one of the challenges of our time. My dissertation highlights some of the challenges in predicting the future composition of communities under climate change, but also provides some ways forward. Integration of experimental, theoretical, and observational studies builds the scaffolding of prediction, whereby understanding the constraints on species physiology, the interactions among species, and community assembly can help frame the context in which predictions are made.

Author: Shaun Turney
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Category :
Languages : en
Pages :

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"Ecological communities are complex, and this complexity can obscure their underlying patterns and natural laws. One way to understand communities is to summarize their most important characteristics using consistent measures. Community structure is a set of measures of composition, abundance, distribution, and interaction that describe an ecological community over space and time. Trophic structure is an important aspect of community structure, and relates to energy and nutrient flow, especially the distribution of organisms across trophic levels. Trophic level is the energetic distance of an organism from the base of production - its average position in the food chains to which it belongs. Due to energetic inefficiencies, we generally predict that organisms decrease in number and biomass with trophic level, forming trophic pyramids (known as "pyramids of numbers" and "pyramids of biomass", respectively). Other, non-pyramidal trophic structures are also common, and trophic structure is affected by variables at multiple ecological scales. The objective of this thesis is to investigate determinants of trophic and community structure, including latitude, ecosystem type, biome transition, community composition, and body size. While pyramids of numbers and pyramids of biomass are well-studied, few have investigated the trophic distribution of diversity. Using a meta-analysis approach, I found that, on average, large published food webs form pyramids of species richness, with a decrease in number of species as trophic level increased. Trophic diversity structure was correlated to centrality, latitude, ecosystem type, and study identity.Community structure varies spatially, as can be seen even by a casual observer at interfaces between biomes. I studied how macroinvertebrate and soil prokaryote communities changed latitudinally along the forest-tundra biome transition in the Yukon, and how the communities responded to other environmental variables. I found that the communities differed between sites, changed along the latitudinal transect, and responded to environmental variables at multiple scales, including active layer depth, lichen cover, and road proximity. Loss of predators can have profound effects on community structure. I used an experimental approach to investigate the effect of spider assemblage composition and diversity on prey consumption. I hypothesized that diverse assemblages would consume more prey due to niche complementarity and sampling effects. I found, however, that the spiders were generalist and intraguild predators, and that the one-species assemblage consumed the most prey. Spider body size affects its trophic niche, energy requirements, and interspecific interactions, and as a result, body size mediates the relationship between spider assemblage composition and prey consumption. The body size of an organism affects how it interacts with other organisms and its biological rates. I used a meta-analytic approach to test several prediction regarding the relationship between body mass and trophic properties of terrestrial vertebrate predators: Accipitridae (hawks, eagles, and their relatives), Felidae (cats), and Serpentes (snakes). I found that the predators chose prey smaller than themselves, within a predictable mass range. Prey taxonomic diversity increased with Serpentes mass. Counter to theory, Felidae trophic level decreased with body mass, and Felidae and Accipitridae predator-prey body mass ratio increased with trophic level. We currently live in the Anthropocene, an epoch characterized by anthropogenic geological, atmospheric, and biological change. These changes are affecting community structure, which in turn is affecting human access to the benefits provided by nature. Therefore, it is important that we continue to study community structure and the variables that affect it, so that we can predict and respond to ecological change in the Anthropocene. " --

Author: Raj Kiran Parmar
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Category : Aquatic invertebrates
Languages : en
Pages : 124

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Land cover change strongly affects biodiversity in stream ecosystems, with several studies demonstrating the negative impacts of agricultural and urban expansion on local community richness. However, little is known of the effects of land cover on the variation among sets of local communities in stream networks, as well as the drivers of community variation in these systems. Using the metacommunity framework, this study takes a multi-scale approach to understand how macroinvertebrate communities are assembled across three catchment land cover types; native forest, agricultural and urban. Specifically, the aims of this study are to assess; (1) how stream network land cover influences alpha and beta diversity of macroinvertebrate communities and, (2) the relative role of local environmental conditions and spatial dispersal variables in structuring these communities. Benthic macroinvertebrate samples and local in-stream and riparian environmental variables were collected at 20 sampling sites in each of the six study stream networks in Auckland. Spatial distance proxies of macroinvertebrate dispersal in stream networks were calculated using geospatial techniques. Community alpha and beta diversity, environmental and distance variables were analysed using multivariate statistical techniques. Comparisons showed reference forest and impacted (agricultural and urban) networks supported distinct communities, with lower alpha diversity in the impacted stream networks. Unexpectedly, beta diversity in the impacted networks was greater than, or equal to the reference stream networks, with community dissimilarity almost entirely driven by species turnover. Overall, irrespective of land cover, macroinvertebrate communities were largely structured by local environmental conditions. Benthic substrate and the presence and composition of riparian vegetation were the most significant local environmental variables influencing community composition. Spatial dispersal limitation variables had a small, but significant, effect on inter-site community dissimilarity and overall community structure in each catchment. Network distance between local communities explained the greatest variation in community dissimilarity of the three distance types. This study identified potential drivers of macroinvertebrate community variation in Auckland streams, specifically highlighting the relative role of local environmental and spatial dispersal processes. The results of this study have relevance for biomonitoring and state of environment reporting of Auckland’s freshwater systems, as well as future stream rehabilitation projects.

Author: Melanie A. Link-Perez
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ISBN:
Category : Biotic communities
Languages : en
Pages :

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Neutral theory recognizes the potential importance of chance and history in the structuring of ecological communities. According to neutral theory, geographic distance should be a predictor of plant community composition, because dispersal limitation is a mechanism contributing to neutral ecological drift. Alternatively, classical niche theory suggests that environmental characteristics determine community composition. I describe the spatial variation in two contrasting prairie communities - one relict, one reconstructed - and compare the observed patterns with predictions derived from neutral and niche theories. I found an important role of ecological drift in the structuring of plant communities at both prairies. Geographic distance explained more variation in species composition than did environmental factors. Although environmental factors are correlated with community composition, the stronger correlations with geographic distance indicate that neutral processes must be taken into account when looking at community structure in small-statured herbaceous communities.

Author: Matthew Scott Schuler
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 115

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The Species Area Relationship (SAR) is one of the oldest and most fundamental patterns in ecology. Researchers have long known that a larger habitat will support more species than a smaller habitat. In the early 20th century, a predictive mathematical model was developed giving researchers an opportunity to understand the consequences of habitat loss for patterns of species richness and diversity. Species richness refers to the number of species observed within a given area. Related to species richness, species diversity is any statistical metric that allows researchers to compare species richness values measured across habitats that have varying probabilities of sampling individuals of the species present. Researchers have used the SAR model to understand the number of species that could be supported by a given amount of habitat, but have also used the SAR to compare the number of species supported by different habitats, to into infer important environmental factors that lead to differences in species richness among habitats. Ecologists have given great attention to studying the roles that these environmental factors play in determining how many species a given habitat will support. Yet, very little consideration has been given to the way in which habitat size alters the effects of those environmental factors on species richness patterns. This dissertation explores the influences that habitat size has on environmental factors that have been proposed as mechanisms that increase or maintain species richness in local habitats. I present three chapters each describing the findings of experiments that explored the interplay between habitat size and three commonly invoked mechanisms that affect local species richness: energy, species dispersal, and habitat heterogeneity. In Chapter 1, I present an experimental test of the species-energy-area relationship, where energy and area are predicted to interact in a positive way to increase the total number of species in a habitat. While much attention has been given to the interaction between habitat size and energy, researchers have failed to recognize that energy input may not be directly acting as a mechanism increasing species richness, but instead increasing the density of individuals, which increases the likelihood of detecting species in high-energy habitats. The 2nd chapter addresses the way in which habitat area alters the importance of dispersal for maintaining species richness in habitats, where small habitats are predicted to benefit more from dispersal than large habitats. Despite classical models in ecology predicting that species dispersal should be most important in small habitats, no conclusive experimental evidence exists showing that habitat size alters the importance of dispersal on species richness in local communities. Finally, in the 3rd chapter I present data from an experiment showing how the importance of habitat heterogeneity depends on habitat size and the aggregation of species among habitats. Habitat heterogeneity has been implicated as one of the most important mechanisms required to increase and maintain species richness in local communities. However, a meta-analysis of heterogeneity experiments revealed that experimental evidence is inconclusive, because many researchers have found positive and negative relationships between habitat heterogeneity and species richness. Additionally, the Area-Heterogeneity-Trade-Off (AHTO) model, developed to predict the relationship between habitat heterogeneity and species richness, has proven to be difficult to test in natural environments, due to the correlation of alternative environmental parameters with habitat heterogeneity. The results of this experiment support the main predictions of the AHTO, but show that the patterns predicted by the model can arise from alternative mechanisms than what the model predicts. The results from the experiments presented within this dissertation advance ecologists' understanding of how environmental variables that are thought to drive patterns of species richness are mediated by the size of the habitat being studied. Furthermore, the results of these experiments add to a longstanding debate in ecology over the importance of habitat size in maintaining species richness. According to the SAR model, the reduction in size of a contiguous habitat will result in an immediate reduction in species richness. Some researchers have suggested, however, that the SAR model always under-predicts the loss of species richness as habitat size decreases. The research presented in this dissertation supports the conclusion that as habitat size decreases, species will be lost at a rate different from the prediction of the SAR model, due to the complex and non-linear relationships between habitat size and environmental factors like energy and heterogeneity that affect the number of species a local habitat could support.

Author: Ashley Christine Lenig
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ISBN:
Category : Stream ecology
Languages : en
Pages : 218

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Author: Guilherme Casas Casas Goncalves
Publisher:
ISBN:
Category :
Languages : en
Pages : 164

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Consumer-resource interactions constitute the fundamental building block of foodwebs, and play an essential role in ecosystem services and biological pest control. The defining feature of consumer-resource interactions is their inherent tendency to oscillate in abundance. This oscillatory tendency can be both weakened and strengthened by abiotic environmental fluctuations such as seasonal temperature variation. My dissertation focuses on the role of abiotic and biotic oscillations mediate the persistence and diversity of consumer-resource communities. I start by investigating how seasonal temperature variation influences the persistence of tritrophic food chains consisting of multicellular ectotherms (invertebrates, fish, amphibians and reptiles). Since ectotherm body temperature depends on the environmental temperature, temperature variation has a direct effect on the physiology, behavior and population dynamics of ectothermic species. I develop a trait-based mathematical framework to investigate tri-trophic interactions amongst ectotherm species inhabiting a seasonally varying thermal environment. By incorporating mechanistic trait response functions --- derived from the first principles of thermodynamics --- into a dynamical model constructed using ordinary differential equations, I find that the persistence of tri-trophic interactions requires that each trophic level be more cold-adapted than the level below it. The model predicts that tri-trophic food chain length should increase with increasing latitude, because higher latitudes experience higher-amplitude seasonal fluctuations and more opportunities for upper trophic levels to be more cold-adapted. Next I expand the framework described above to develop predictions of how developmentally induced time delays affect niche partitioning in seasonal environment, using delay differential equations (DDEs) to capture the effects of temperature dependent maturation rates. I find that developmental delays reduce opportunities for thermal niche partitioning by reducing the temporal separation between species, since juveniles keep maturing after the environment has become unfavorable for the focal species and favorable for its competitor. The addition of developmental delays also leads to the emergence of uninvasible attack optimum or response breadth values which maximize the overlap between the consumer species' lifetime reproductive success and the resource's fundamental thermal niche. While these uninvasible strategies preclude niche partitioning, such partitioning becomes possible when species vary in their attack optima or response breadth \textit{and} temperature sensitivity of juvenile or adult mortality. Finally, I study how stage structure and delayed negative feedback affect coexistence through relative nonlinearity. I use a DDE based model with in a constant thermal environment, using trait species values based on data from the harlequin bug and one of its parasitoids. I find that the presence of stage structure hinders coexistence through relative nonlinearity, since it reduces the differences in resource oscillations generated by consumers with different functional responses. This result is not generated by delayed application of negative feedback, and I posit that it is instead the delayed application of the positive feedback. The work I present here addresses the interplay between a community's abiotic and biotic environments, with the latter encompassing both species life history and community structure. The frameworks developed here are based on first principles, which allows me to make general predictions on community structure, and can be parameterized with species specific data that can predict the outcomes of specific interactions. The data I use on our models include systems with important applications for pest control, so the results here can be applied to specific systems of high economic importance. Taken together, this dissertation represents a step towards a framework that advances our theoretical understanding of natural communities and their environments and has important practical applications.

Author: Courtney Lynn Davis
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ISBN:
Category :
Languages : en
Pages :

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The effects of environmental change on individual species depend on interactions between climate, other co-occurring species, and the physical environment in which interactions occur. Despite this, commonly used methods for predicting species' responses to environmental change, such as bioclimatic envelope models, do not consider community dynamics or complex interactions between climate and the physical environment, making it difficult to predict how species distributions and community assemblages will be affected. The work presented in this dissertation uses novel or recently developed hierarchical modeling approaches to make inference about the dynamic processes structuring populations and communities, with a specific focus on understanding: 1) how species interact with one another across the landscape; 2) how species interact with their environment; and 3) how climate influences these interactions. In my first chapter, I analyzed camera trap data for 108,087 trap days across 12 countries spanning 5 continents to better understand how mammalian carnivore communities are structured globally. I used a two-species occupancy modeling approach to estimate local probabilities of co-occurrence among 768 species pairs from the order Carnivora and evaluate how shared ecological traits (e.g., activity pattern, diet, body size) correlate with probabilities of co-occurrence. I found that species pairs co-occurred more frequently than expected at random within individual study areas. Co-occurrence probabilities were greatest for species pairs that shared ecological traits including similar body size, temporal activity pattern, and diet. This indicates that shared habitat affinities are likely more important than niche separation in structuring carnivore communities. However, co-occurrence decreased as compared to other species pairs when the pair included a large-bodied carnivore. These results suggest that a combination of shared traits and top-down regulation by large carnivores shape local carnivore communities. This chapter represents the first global assessment of carnivore spatial co-occurrence patterns and provides a framework for other collaborative, global-scale studies on interactions among species. The novelty of my study comes in the ability to assess how these important communities are organized across the globe. Global monitoring efforts and analyses such as these are vital to understanding the underlying processes of community structure and assembly, as well as the conservation of wildlife populations at local, regional, and global scales. In my second chapter, I used data from a 6-year capture-mark-recapture study (2014 to 2019) of adult spotted salamanders (Ambystoma maculatum) in central Pennsylvania, USA, to estimate population connectivity among breeding wetlands. I quantified inter- and intra-annual site fidelity, breeding dispersal probabilities as a function of distance between wetlands, abundance, and annual survival using a multistate, hidden Markov estimator. I found that inter-annual site fidelity of males varied among wetlands and was positively associated with population density. Females exhibited higher inter-annual site fidelity and dispersed further than males between breeding seasons. Within breeding seasons, I found that up to 6% of males dispersed to a new wetland each day. These results indicate high population connectivity and suggest that long-term population persistence in this study system will depend on maintaining wetlands that vary in size, hydroperiod and spatial proximity. This chapter represents the first study to directly compare amphibian breeding dispersal probabilities and distances at multiple scales, and provides a robust framework for improving inference on the spatial and temporal patterns of amphibian movement. Lastly, in my third chapter, I used multi-species occupancy and structural equation modeling approaches to quantify the direct and indirect effects of extreme weather events on a coastal freshwater wetland system. I used data from an 8-year study (2009 to 2016) on St. Marks National Wildlife Refuge in Florida, USA, to quantify species-specific and community-level changes in amphibian and fish occupancy associated with extreme flooding events in 2012 and 2013. Specifically, I examined how physical changes to the landscape, including changes in salinity and increased wetland connectivity, may have contributed to or exacerbated the effects of these extreme weather events on the biota of isolated coastal wetlands. I was able to demonstrate that the indirect effects of flooding on amphibians, via changes in the composition of the fish community and salinity, were species-specific and driven, at least in part, by life history traits (e.g., breeding strategy). These extreme weather events led to an overall decline in local amphibian species richness observed from 2009 to 2016, suggesting that coastal wetland-breeding communities on St. Marks may not be resilient to the predicted changes in disturbance regimes as a result of climate change. In combination with long-term monitoring data, the integrated framework I developed in this chapter allows for more robust predictions regarding the ecosystem-level impacts of a changing climate. With recent efforts to coordinate, consolidate and integrate ecological data from various ecosystems across large temporal and spatial scales, there is a huge demand for efficient yet effective statistical tools. Each of the three chapters described above use a different hierarchical modeling approach to make inference about the processes structuring populations and communities, while accounting observational uncertainty. The work presented in this dissertation further develops the utility and accessibility of these methods, such that other ecologists can use these tools to better understand population- and community-level responses to variable environments and changing conditions.

Author: Janet Franklin
Publisher:
ISBN: 9780511765605
Category :
Languages : en
Pages : 320

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