Food webs Research Papers - Academia.edu (original) (raw)

Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species... more

Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species interaction patterns. Here, we integrate stable isotope analysis and network theory to reconstruct patterns of trophic interactions for six independent mammalian communities that inhabited mammoth steppe environments spanning western Europe to eastern Alaska (Beringia) during the Late Pleistocene. We use a Bayesian mixing model to quantify the contribution of prey to the diets of local predators, and assess how the structure of trophic interactions changed across space and the Last Glacial Maximum (LGM), a global climatic event that severely impacted mammoth steppe communities. We find that large felids had diets that were more constrained than those of co-occurring predators, and largely influenced by an increase in Rangifer abundance after the LGM. Moreover, the structural organization of Beringian and European communities strongly differed: compared with Europe, species interactions in Beringian communities before—and possibly after—the LGM were highly modular. We suggest that this difference in modularity may have been driven by the geographical insularity of Beringian communities.

The central organizing theme of this paper is to discuss the dynamics of the Serengeti grassland ecosystem from the perspective of recent developments in food-web theory. The seasonal rainfall patterns that characterize the East African... more

The central organizing theme of this paper is to discuss the dynamics of the Serengeti grassland ecosystem from the perspective of recent developments in food-web theory. The seasonal rainfall patterns that characterize the East African climate create an annually oscillating, large-scale, spatial mosaic of feeding opportunities for the larger ungulates in the Serengeti; this in turn creates a significant annual variation in the food available for their predators. At a smaller spatial scale, periodic fires during the dry season create patches of highly nutritious grazing that are eaten in preference to the surrounding older patches of less palatable vegetation. The species interactions between herbivores and plants, and carnivores and herbivores, are hierarchically nested in the Serengeti food web, with the largest bodied consumers on each trophic level having the broadest diets that include species from a large variety of different habitats in the ecosystem. The different major habi...

The diversity of life is ultimately generated by evolution, and much attention has focused on the rapid evolution of ecological traits. Yet, the tendency for many ecological traits to instead remain similar over time [niche conservatism... more

The diversity of life is ultimately generated by evolution, and much attention has focused on the rapid evolution of ecological traits. Yet, the tendency for many ecological traits to instead remain similar over time [niche conservatism (NC)] has many consequences for the fundamental patterns and processes studied in ecology and conservation biology. Here, we describe the mounting evidence for the importance of NC to major topics in ecology (e.g. species richness, ecosystem function) and conservation (e.g. climate change, invasive species). We also review other areas where it may be important but has generally been overlooked, in both ecology (e.g. food webs, disease ecology, mutualistic interactions) and conservation (e.g. habitat modification). We summarize methods for testing for NC, and suggest that a commonly used and advocated method (involving a test for phylogenetic signal) is potentially problematic, and describe alternative approaches. We suggest that considering NC: (1) focuses attention on the within-species processes that cause traits to be conserved over time, (2) emphasizes connections between questions and research areas that are not obviously related (e.g. invasives, global warming, tropical richness), and (3) suggests new areas for research (e.g. why are some clades largely nocturnal? why do related species share diseases?).

Network biology is a science that deals with the structure, function, regulation (control), design, and application, etc., of various biological networks. It is an interdisciplinary science based on life sciences (biology, ecology,... more

Foodwebs are nowadays an interesting and challenging subject of study for network analysis. In this study real food webs are compared one to each other in terms of how authors collected data, in order to build a coherent dataset. Emergent... more

Foodwebs are nowadays an interesting and challenging subject of study for network analysis. In this study real food webs are compared one to each other in terms of how authors collected data, in order to build a coherent dataset. Emergent patterns of these food webs are then quantified and three different generative models are used to try to reproduce them: cascade model, niche model and nested hierarchy model. A detailed comparison shows how niche model is the most suited of the three in accord with the data. Finally, an original clustering algorithm based on the idea of pollution spread is proposed and studied over food webs generated with the niche model. This algorithm needs no parameters, is suited for directed networks and provides information on which species may be screened to understand if the considered food web is polluted.

Understanding the ecological role of a species in an ecosystem and the dynamics of the communities depends largely on knowledge of the trophic relationships. We evaluated the feeding habits and the trophic ecology of the endemic Colombian... more

Understanding the ecological role of a species in an ecosystem and the dynamics of the communities depends largely on knowledge of the trophic relationships. We evaluated the feeding habits and the trophic ecology of the endemic Colombian stingray Potamotrygon magdalenae, integrating stomach content and isotopic analyses (13 C and 15 N). The samples were collected in the middle Magdalena River basin, Colom-bia, during artisanal fishing operations in the dry and rainy seasons. The stomach content analysis indicated that P. magdalenae fed on a high number of occasional items, such as seeds, Planariidae, Teleostei and Nema-toda, with Diptera being the dominant food component at the population level. There were no significant differences in diet between males and females. In contrast, isotopic analysis showed that Coleoptera was the most important food source assimilated by the species, followed by Ephemeroptera; Chironomidae and Tri-choptera made the lowest contributions. No significant differences in δ 13 C and δ 15 N were observed between the sexes or hydrological seasons. Estimates of the isotopic niche indicated that P. magdalenae has a narrower tro-phic niche than the teleost fishes present in the study area. The trophic level was identified as intermediate, suggesting that Potamotrygon magdalenae plays a role as a mesopredator in the food web in the study area.

Food webs based on dead organic matter have received relatively little research attention. Here we focus on dead-wood-dependent (saproxylic) arthropod communities—an overlooked component of forest biodiversity that contributes to... more

Food webs based on dead organic matter have received relatively little research attention. Here we focus on dead-wood-dependent (saproxylic) arthropod communities—an overlooked component of forest biodiversity that contributes to decomposition of fallen trees and nutrient cycling. First, we summarized information on factors that impact saproxylic arthropod biodiversity via a descriptive mini-review of the literature, given that the structure of food webs should be contingent upon local community composition, species richness, and/or species abundances within and among neighboring rotting logs. Next, we coupled intensive fieldwork with molecular approaches to taxonomic identification of saproxylic arthropods sampled from rotting logs in the southern Appalachian Mountains, and synthesized information on their feeding ecology, in order to infer trophic interactions. Our descriptive mini-review highlighted major influences of local-scale (site-specific) factors affecting biodiversity, and by extension, food web structure; a pronounced publication bias toward saproxylic beetles from evergreen forests in Europe was also evident. Our empirical data on community composition of rotting logs at intermediate to late stages of decay revealed a complex food web structure. This comprised internal and external primary nutrient sources (dead wood within logs vs. nearby living trees and fallen leaves), a diverse suite of primary consumers (wood-feeding detritivores, leaf litter-feeding detritivores, as well as herbivores and fungivores), several secondary consumer functional groups (omnivorous scavengers and ectoparasites or parasitoids), and top-level carnivorous predators that were mostly made up of spiders, Opiliones, and centipedes. We close by discussing persistent challenges and limitations, and suggest future research directions.

To properly conserve, restore and manage riverine ecosystems and the services they provide, it is pertinent to understand their functional dynamics. Growing human populations and high dependency on natural resources in developing... more

To properly conserve, restore and manage riverine ecosystems and the services they provide, it is pertinent to understand their functional dynamics. Growing human populations and high dependency on natural resources in developing countries have exerted pressure on land and water resources. However, there is a major knowledge gap concerning the influence of human activities and wildlife on the functioning of tropical rivers in terms of organic matter input, processing and energy sources supporting riverine consumers. This thesis explores the functioning of tropical upland streams and savanna rivers by assessing the spatial and temporal dynamics in organic matter processing under different land-use and discharge conditions and the resultant influence on energy sources for riverine consumers. This thesis contributes to the theories of river functioning and has improved understanding of the functioning of African tropical streams by identifying a diverse macroinvertebrate shredder guild...

The benthic foodweb structure of Lake Võrtsjärv, a large (270 km2), shallow, and turbid Estonian lake, was evaluated based on C and N stable-isotope signatures (δ13C, δ15N). Variation in δ13C between sampling sites was not related to site... more

The benthic foodweb structure of Lake Võrtsjärv, a large (270 km2), shallow, and turbid Estonian lake, was evaluated based on C and N stable-isotope signatures (δ13C, δ15N). Variation in δ13C between sampling sites was not related to site proximity to the littoral zone or the more vegetated southern part of the lake, but rather appeared to be influenced by in-situ site peculiarities. δ13C was stable temporally and between functional feeding groups, a result implying that the whole benthic food web of the lake relies largely on the same C source admixture, essentially particulate organic matter (POM). Thus, the foodweb composition of Lake Võrtsjärv is remarkably homogeneous given the lake’s large surface area. Apparent trophic-level δ15N fractionation between total collectors and total predators (mean 1.7‰) was lower than the value of 3.4‰ generally adopted in foodweb studies, but the higher value was valid for specific prey–predator links. The low δ13C signature of some chironomid samples indicated probable assimilation of methane-oxidizing bacteria (MOB) by these sediment-dwelling invertebrates. However, the lack of similar 13C depletion in benthic filterers (mussels) indicated that the MOB layer is essentially confined to the sediments and does not reach the water column, which probably constrains transfer of methane-derived C through the food web to fish in this lake. Our study demonstrates that the benthic food web of shallow turbid lakes like Võrtsjärv is simplified and is mostly sustained by phytoplanktonic C sources.

Riverine habitats are vulnerable to a host of environmental stressors, many of which are increasing in frequency and intensity across the globe. Climate change is arguably the greatest threat on the horizon, with serious implications for... more

Riverine habitats are vulnerable to a host
of environmental stressors, many of which are
increasing in frequency and intensity across the
globe. Climate change is arguably the greatest threat
on the horizon, with serious implications for freshwater
food webs via alterations in thermal regimes,
resource quality and availability, and hydrology. This
will induce radical restructuring of many food webs,
by altering the identity of nodes, the strength and
patterning of interactions and consequently the
dynamics and architecture of the trophic network as
a whole. Although such effects are likely to be
apparent globally, they are predicted to be especially
rapid and dramatic in high altitude and latitude
ecosystems, which represent ‘sentinel systems’. The
complex and subtle connections between members of
a food web and potential synergistic interactions with
other environmental stressors can lead to seemingly
counterintuitive responses to perturbations that cannot
be predicted from the traditional focus of
studying individual species in isolation. In this
review, we highlight the need for developing new
network-based approaches to understand and predict
the consequences of global change in running waters.

The potential impacts of changes in precipitation patterns associated with global climate change on the relationship between soil community diversity and litter decomposition were investigated. For a period of ca. 5 months, two decomposer... more

The potential impacts of changes in precipitation patterns associated with global climate change on the relationship between soil community diversity and litter decomposition were investigated. For a period of ca. 5 months, two decomposer communities in litterbags (1000 and 45 μm mesh size) containing spruce litter were subjected to two irrigation treatments: constant and fluctuating (drying/rewetting) moisture conditions. The latter were expected to induce moisture stress on the decomposer communities. The two mesh sizes were used to exclude different faunal components from the decomposer communities. The 1000 μm mesh excluded only the macrofauna, whereas the 45 μm mesh excluded both the macro- and mesofauna. In the short-term perspective of the present study, mesofauna abundance showed no response to imposed fluctuating moisture conditions. Irrespective of the presence of mesofauna, mass loss, microbial biomass and the control mechanisms, regulating carbon mineralization appeared unaffected by fluctuating moisture conditions. The reduction in the functional/structural diversity of the decomposer communities in the 45 μm litterbags resulted in strongly increased Nematoda abundance but it did not alter the response of Nematoda to fluctuating moisture conditions. Processes in the nitrogen (N)-cycle and mass loss were sensitive indicators of changes in the structural and functional complexity of decomposer communities. However, a negative effect of fluctuating moisture conditions on extractable N was coupled to the presence of mesofauna. Extremes in rainfall patterns, generated by climate change, may have a negative impact on the availability of nutrients, particularly N, for plants. This effect could be amplified by an additional impoverishment in the structural and functional complexity of the respective decomposer communities.

Policy paper that describes the possible consequences of building a road through the Serengeti National Park and suggests that an alternative road to the south of the ecosystem as it would provide infrastructure and access to vital... more

Policy paper that describes the possible consequences of building a road through the Serengeti National Park and suggests that an alternative road to the south of the ecosystem as it would provide infrastructure and access to vital markets for nearly ten times as many people without casuing excessive damage to one of the world's most pristine ecosystems.

This study presents isotopic data (d13C and d15N from bone collagen) for 104 samples representing 29 vertebrate taxa from late pre-contact through to contact era (ca. 2000 – 100 BP) Haida Gwaii (British Columbia, Canada) from a wide... more

This study presents isotopic data (d13C and d15N from bone collagen) for 104 samples representing 29 vertebrate taxa from late pre-contact through to contact era (ca. 2000 – 100 BP) Haida Gwaii (British Columbia, Canada) from a wide variety of mostly marine organisms. The results demonstrate the considerable isotopic variability that characterizes potential prey items in coastal contexts and underscores the need for baseline faunal data to interpret human subsistence practices. Based on these data, a detailed marine food web was constructed, which provides insight into local ecological conditions. We present a simple method for quantifying the trophic level of ancient fauna using d15N of bone collagen. Finally, we discuss the implications of this study for the reconstruction of human diet.

Niche segregation between introduced and native fish in Lake Nahuel Huapi, a deep oligotrophic lake in Northwest Patagonia (Argentina), occurs through the consumption of different prey. Therefore, in this work we analyzed total mercury... more

Niche segregation between introduced and native fish in Lake Nahuel Huapi, a deep oligotrophic lake in Northwest Patagonia (Argentina), occurs through the consumption of different prey. Therefore, in this work we analyzed total mercury [THg] and methylmercury [MeHg] concentrations in top predator fish and in their main prey to test whether their feeding habits influence [Hg]. Results indicate that [THg] and [MeHg] varied by foraging habitat and they increased with greater percentage of benthic diet and decreased with pelagic diet in Lake Nahuel Huapi. This is consistent with the fact that the native creole perch, a mostly benthivorous feeder, which shares the highest trophic level of the food web with introduced salmonids, had higher [THg] and [MeHg] than the more pelagic feeder rainbow trout and bentho-pelagic feeder brown trout. This differential THg and MeHg bioaccumulation observed in native and introduced fish provides evidence to the hypothesis that there are two main Hg transfer pathways from the base of the food web to top predators: a pelagic pathway where Hg is transferred from water, through plankton (with Hg in inorganic species mostly), forage fish to salmonids, and a benthic pathway, as Hg is transferred from the sediments (where Hg methylation occurs mostly), through crayfish (with higher [MeHg] than plankton), to native fish, leading to one fold higher [Hg].

Three Ghanaian reservoirs (Tono, Bontanga and Golinga) were compared through a food web modelling approach (Ecopath with Ecosim) to assess production characteristics and food web structures. The lakes differ in size and morphology,... more

Three Ghanaian reservoirs (Tono, Bontanga and Golinga) were compared through a food web modelling approach (Ecopath with Ecosim) to assess production characteristics and food web structures. The lakes differ in size and morphology, generating specific conditions for fish growth and production. While the two top fishery target species were Sarotherodon galilaeus (L.) and Oreochromis niloticus (L.) in all reservoirs, the mean trophic level of the catch was lowest in the largest and deepest reservoir (Tono) due to higher trophic level species occupying less accessible deep “refuge” habitats. The smallest lake had the highest fish production under optimal conditions of water supply (17.1 compared with 15.5 and 10.1 t/km2/year for lakes Bontanga and Tono), but it appears to be most vulnerable under conditions of drought. For the planning and construction of adequately sized reservoirs used for fishery and irrigation purposes, the water budget (ratio of inflow and evaporation) needs to be estimated.

Competing hypotheses explaining species’ use of resources have been advanced. Resource limitations in habitat and/or food are factors that affect assemblages of species. These limitations could drive the evolution of morphological and/or... more

Competing hypotheses explaining species’ use of resources have been advanced.
Resource limitations in habitat and/or food are factors that affect assemblages of species.
These limitations could drive the evolution of morphological and/or behavioural
specialization, permitting the coexistence of closely related species through resource
partitioning and niche differentiation. Alternatively, when resources are unlimited,
fluctuations in resources availability will cause concomitant shifts in resource use
regardless of species identity. Here, we used next-generation sequencing to test these
hypotheses and characterize the diversity, overlap and seasonal variation in the diet of
three species of insectivorous bats of the genus Pteronotus. We identified 465 prey
(MOTUs) in the guano of 192 individuals. Lepidoptera and Diptera represented the
most consumed insect orders. Diet of bats exhibited a moderate level of overlap, with
the highest value between Pteronotus parnellii and Pteronotus personatus in the wet
season. We found higher dietary overlap between species during the same seasons
than within any single species across seasons. This suggests that diets of the three species
are driven more by prey availability than by any particular predator-specific characteristic.
P. davyi and P. personatus increased their dietary breadth during the dry
season, whereas P. parnellii diet was broader and had the highest effective number of
prey species in all seasons. This supports the existence of dietary flexibility in generalist
bats and dietary niche overlapping among groups of closely related species in
highly seasonal ecosystems. Moreover, the abundance and availability of insect prey
may drive the diet of insectivores.