Impact of cyber-invasive species on a large ecological network

As impacts of introduced species cascade through trophic levels, they can cause indirect and counter-intuitive effects. To investigate the impact of invasive species at the network scale, we use a generalized food web model, capable of propagating changes through networks with a series of ecologically realistic criteria. Using data from a small British offshore island, we quantify the impacts of four virtual invasive species (an insectivore, a herbivore, a carnivore and an omnivore whose diet is based on a rat) and explore which clusters of species react in similar ways. We find that the predictions for the impacts of invasive species are ecologically plausible, even in large networks. Species in the same taxonomic group are similarly impacted by a virtual invasive species. However, interesting differences within a given taxonomic group can occur. The results suggest that some native species may be at risk from a wider range of invasives than previously believed. The implications of these results for ecologists and land managers are discussed

Global plant characterisation and distribution with evolution and climate

Since Arrhenius published seminal work in 1921, research interest in the description of plant traits and grouped characteristics of plant species has grown, underpinning diversity in trophic levels. Geographic exploration and diversity studies prior to and after 1921 culminated in biological, chemical and computer-simulated approaches describing rudiments of growth patterns within dynamic conditions of Earth. This thesis has two parts:- classical theory and multidisciplinary fusion to give mathematical strength to characterising plant species in space and time.Individual plant species occurrences are used to obtain a Species-Area Relationship. The use of both Boolean and logic-based mathematics is then integrated to describe classical methods and propose fuzzy logic control to predict species ordination. Having demonstrated a lack of significance between species and area for data modelled in this thesis a logic based approach is taken. Mamdani and T-S-K fuzzy system stability is verified by application to individual plant occurrences, validated by a multiple interfaced data portal. Quantitative mathematical models are differentiated with a genetic programming approach, enabling visualisation of multi-objective dispersal of plant strategies, plant metabolism and life-forms within the water-energy dynamic of a fixed time-scale scenario. The distributions of plant characteristics are functionally enriched through the use of Gaussian process models. A generic framework of a Geographic Information System is used to visualise distributions and it is noted that such systems can be used to assist in design and implementation of policies. The study has made use of field based data and the application of mathematic methods is shown to be appropriate and generative in the description of characteristics of plant species, with the aim of application of plant strategies, life-forms and photosynthetic types to a global framework. Novel application of fuzzy logic and related mathematic method to plant distribution and characteristics has been shown on a global scale. Quantification of the uncertainty gives novel insight through consequent trophic levels of biological systems, with great relevance to mathematic and geographic subject development. Informative value of Z matrices of plant distribution is increased substantiating sustainability and conservation policy value to ecosystems and human populations dependent upon them for their needs.Key words: sustainability, conservation policy, Boolean and logic-based, fuzzy logic, genetic programming, multi-objective dispersal, strategies, metabolism, life-forms

Can Ecological Interactions be Inferred from Spatial Data?

The characterisation and quantication of ecological interactions, and the construction of species distributions and their associated ecological niches, is of fundamental theoretical and practical importance. In this paper we give an overview of a Bayesian inference framework, developed over the last 10 years, which, using spatial data, offers a general formalism within which ecological interactions may be characterised and quantied. Interactions are identied through deviations of the spatial distribution of co-occurrences of spatial variables relative to a benchmark for the non-interacting system, and based on a statistical ensemble of spatial cells. The formalism allows for the integration of both biotic and abiotic factors of arbitrary resolution. We concentrate on the conceptual and mathematical underpinnings of the formalism, showing how, using the Naive Bayes approximation, it can be used to not only compare and contrast the relative contribution from each variable, but also to construct species distributions and niches based on arbitrary variable type. We show how the formalism can be used to quantify confounding and therefore help disentangle the complex causal chains that are present in ecosystems. We also show species distributions and their associated niches can be used to infer standard "micro" ecological interactions, such as predation and parasitism. We present several representative use cases that validate our framework, both in terms of being consistent with present knowledge of a set of known interactions, as well as making and validating predictions about new, previously unknown interactions in the case of zoonoses

Predator decline leads to decreased stability in a coastal fish community

Fisheries exploitation has caused widespread declines in marine predators. Theory predicts that predator depletion will destabilise lower trophic levels, making natural communities more vulnerable to environmental perturbations. However, empirical evidence has been limited. Using a community matrix model, we empirically assessed trends in the stability of a multispecies coastal fish community over the course of predator depletion. Three indices of community stability (resistance, resilience and reactivity) revealed significantly decreasing stability concurrent with declining predator abundance. The trophically downgraded community exhibited weaker top-down control, leading to predator-release processes in lower trophic levels and increased susceptibility to perturbation. At the community level, our results suggest that high predator abundance acts as a stabilising force to the naturally stochastic and highly autocorrelated dynamics in low trophic species. These findings have important implications for the conservation and management of predators in marine ecosystems and provide empirical support for the theory of predatory control

Report of the Study Group on Modelling of Physical/Biological Interaction [La Rochelle, France, 5- 7 March, 2001]

Contributor: Einar Svendse

Invasion of a stream food web by a new top predator.

PhDA large predator, the nymph of the dragonfly Cordulegaster boltonii (Anisoptera) (Donovan), has recently invaded Broadstone Stream, an acid headwater in southern England. Because of its large size, the invader established itself as a new top predator. The Broadstone Stream food web is exceptionally detailed and the community has been studied since the early 1970s. The invasion of C boltonii, therefore, provided a rare opportunity to investigate the effects of a potentially strong perturbation upon a well-described system. At the peak of the invasion C boltonii density exceeded seventy nymphs per square metre, comparable to the abundance of the previous top predators. The invasion appeared to part of a long-term trend, within an otherwise persistent community, towards a fauna less tolerant of profound acidity. Mobile, epibenthic prey were particularly vulnerable to C boltonii, due to high encounter rate. In field experiments,t he invader depressedth e abundanceo f two such species, a previous top predator and a detritivorous stonefly, whereas many other taxa were largely unaffected. Predator impact was strongest during peak prey abundance in the summer and autumn, and weakest in the spring when prey were scarce. The diets of the resident predators and C boltonii overlapped extensively when prey were seasonally abundant, but resource-partitioning increased as prey abundance declined. The recent decline in the abundance of P. conspersa, which had the most similar diet to C boltonfl, may be due to competitive and predatory interactions with the larger predator. Cordulegaster boltonii preyed upon virtually every animal taxon within the food web. Consequently, the complexity of the web (e. g. linkage density, omnivory and chain length) increased following the invasion. However, most taxa were rare and most feeding links were weak when the web was quantified.Natural Environment Research Counci

Food webs in the lower Waikato River and the role of hydrogeomorphic complexity

Large rivers are fundamental to human societies and consequently their ecosystems have come under increasing pressure from a range of developments and uses. Despite this, there is still a major knowledge gap understanding food webs supporting fisheries of large river ecosystems. Quantifying the contributions of carbon sources that support food webs is an important and growing field of ecological research, with implications for future management and rehabilitation of large rivers. I reviewed theoretical concepts addressing carbon flow in large river food webs where organic matter from floodplains (Flood Pulse Concept), local aquatic sources (Riverine Productivity Model), or leakage from upstream processing of terrestrial organic matter (River Continuum Concept) can fuel secondary production. Recent empirical evidence highlights the importance of autochthonous carbon, especially in the form of benthic algae and phytoplankton, to food webs in a variety of large rivers along with a range of secondary carbon sources that can assume importance depending on temporal and spatial variation in hydrogeomorphic conditions. The geographic spread of studies addressing carbon flow in large river food webs is steadily increasing, although information remains sparse on temperate Southern Hemisphere rivers and long-term data sets on carbon flow are generally lacking. I measured natural abundances of stable carbon (δ13C) and nitrogen (δ15N) isotopes to quantify spatial and temporal patterns of carbon flow through aquatic food webs in the lowland section of New Zealand’s longest river, the Waikato River. Zones of potential ecological importance influencing carbon transfer along the lower Waikato River were identified using a combination of (i) high-frequency, along-river water quality measurements collected during four seasons and (ii) river channel morphology data derived from aerial photos. A multivariate statistical approach was developed to identify three hydrogeomorphic zones shaped by the physical complexity and channel character of constituent river reaches, and characterised by shifts, sometimes transitional, of physico-chemical variables. Changes in water clarity, chlorophyll fluorescence and specific conductance were driven by tributary inflows and tidal influence. Carbon flow estimated using the mixing model IsoSource supported predictions of the Riverine Productivity Model, with autochthonous algae and biofilms (phytomicrobenthos) the most important basal carbon sources contributing to consumer biomass in all three zones. These sources were often supported by C3 aquatic macrophytes and allochthonous C3 riparian plants. However, the relative importance of organic carbon sources appeared to change depending on season and zone, likely in response to variations in water temperature and flow, particularly in the unconstrained zone of the lower river. It was also demonstrated that to draw robust conclusions, consideration must be given to quantifying the isotopic signatures of organisms lower in the food web, as these can change significantly between sampling times and hydrogeomorphic zones. Tributary confluences can be hotspots for biological production and provide novel carbon sources from donor sub-catchments in large river systems. Littoral food webs and water quality were compared between two main stem habitats (constrained and unconstrained hydrogeomorphic zones) and tributary junctions representing those fed by streams, lakes and wetlands during seasonal low flows when these habitats were likely to be most different. δ13C and δ15N isotopes were then employed using the Bayesian statistics R package Stable Isotope Analysis in R (SIAR) to estimate carbon flow through food webs and also to estimate measures of trophic structure. Pathways were also tested using analysis of fish stomach contents. SIAR mixing models confirmed that autochthonous benthic carbon was the most important carbon source to littoral food webs in all habitats. Riparian carbon appeared to be the most important secondary carbon source to fish consumers, and estimates of its contribution were often greater in tributary junctions compared to fish of the same species in the main stem. Trophic patterns of fish species collected in both the main stem and tributary junctions were similar amongst habitats, as were community metrics estimated using stable isotope signatures and SIAR. This study demonstrates that, while they may add to the lateral complexity of the riverscape, permanently connected habitats such as tributary junctions do not necessarily contribute to overall food web complexity. In this study tributary junctions tended to be steep-sided, and complex littoral habitats containing woody debris and macrophytes were typically rare, potentially limiting the development of more complex food webs. These results contribute to the ever-improving data regarding food web ecology in large rivers, particularly with regard to carbon flow, and the role played by lateral habitats and hydrogeomorphic zones in shaping these processes. This study also provides information and recommendations that provide direction for future research and management actions aimed at aiding the rehabilitation of the lower Waikato River, its riverscape and biological communities

Stable isotope data as reef food-web descriptors in a dynamic tropical environment

PhD ThesisDespite the increasing use of stable isotope data as diet and trophic position descriptors in food-web ecology, their generic value relies on basic assumptions of constant trophic step enrichment, steady state conditions and accuracy of isotopic analyses for the estimation of trophic level (TL). This thesis explores the implications of these assumptions for understanding reef community trophodynamics in Oman, where upwelling events produce seasonal patterns among potential food sources. Nitrogen isotopes (δ15N) revealed 3-4 TL’s (6.16 to 17.8‰) and the wide range of carbon isotope (δ13C) values (-21.92 to -6.43‰) indicated that there were both benthic and pelagic sources of production. Primary producer and primary consumer δ15N fluctuated seasonally by 2.24‰ (9.02-11.26‰) however, this variability was not consistently observed at higher TLs, and therefore the δ15N of high-TL consumers may not accurately reflect their trophic position. Long-lived marine bivalves had no temporal isotopic variability, allowing the trophic position of higher consumers to be estimated using their δ15N as a baseline. Baseline organisms also allowed spatial comparison of part of the trophic structure of two reef communities; Barr al Hickman had δ15N values 2.7‰ enriched compared to a similar community at Bandar Kayran 360km to the north. Across the Western Indian Ocean, macroalgae δ15N values correlated well with differences in underlying nutrient regimes of surrounding waters. Trophic-step fractionation in herbivorous fish was 4.69-5.25‰, higher than the generally accepted value of 3.4‰ and was explained by a dynamic model incorporating feeding rate, diet quality and excretion rate, which are inherently different between herbivorous and carnivorous fish. δ15N was strongly correlated with body size in some fish species but across the entire community body size was a poor descriptor of trophic position. Use of dietspecific trophic-step fractionation values and sulphur isotopes (δ34S) greatly improved the resolution of food-web models.NERC CASE Newcastle University Centre for Environment Fisheries and Aquaculture Sciences (CEFAS

Linking biotic activity to ecosystem functioning

Merged with duplicate record 10026.1/2441 on 14.03.2017 by CS (TIS)The central theme of this thesis was the search for ecologically meaningful ways to quantify the relationships between the biota and ecosystem processes. This thesis investigated whether a "functional group" approach, that characterised the fauna according to similarities in their activities, could be successfully employed to quantifiably link species' performance to important ecosystem processes. Initially the abilities of traditional "trophic" and "bioturbatory" categories to characterise the estuarine macrobenthic fauna and discriminate between estuarine sites were examined. This thesis determined that the perceived inter-site similarity within an estuary varied according to the function being investigated and that the apparent associations between abiotic factors and biotic assemblages were also heavily influenced by the choice of functional classification. This study provided strong evidence that links between the macrobenthos and abiotic factors were most easily detected if the species were grouped according to their bioturbatory abilities. Thus, attempts to model the contribution of the estuarine macrofauna to sediment mixing throughout an estuary were pursued in preference to modelling trophic group distribution. This thesis identified limitations of existing "bioturbation" categories and hence, developed a novel classification system that incorporated species' activity rates, magnitude and location within the sediment. Strong evidence was found that estuarine macrobenthic communities should be treated as two separate assemblages: one shallow assemblage occupying surface and near surface layers, and one deep assemblage with the ability to exploit the sediment at greater depths. The two separate assemblages displayed different associations with the environmental factors examined in this study. By developing new functional groupings of species' behaviour, and treating shallow and deep assemblages as separate entities, this thesis was able to estimate the contribution of the biota to sediment mixing and successfully develop and validate generic predictive models of functional group distribution within the Tamar/Plym estuarine system. Since the functional groups themselves convey information about the magnitude of their effect and the sediment horizons impacted, this thesis represents an important advance in our ability to predict biological contribution to sediment mixing processes in estuarine ecosystems.Plymouth Marine Laborator