Browsing by Subject "ECOLOGICAL NETWORKS"

Sort by: Order: Results:

Now showing items 1-4 of 4
  • Frelat, Romain; Kortsch, Susanne; Kroencke, Ingrid; Neumann, Hermann; Nordstroem, Marie C.; Olivier, Pierre E. N.; Sell, Anne F. (2022)
    Ecological communities are constantly changing as a response to environmental and anthropogenic pressures. Yet, how changes in community composition influence the structure of food webs over time and space remains elusive. Using ecological network analysis, we assessed how food web structure changed across six distinct areas of the North Sea over a sixteen-year time-period. We used multivariate analyses to disentangle and compare spatio-temporal dynamics in community composition (i.e. changes in species abundances) and food web structure (i.e. changes in network properties). Specifically, we assessed how changes in community composition were reflected in food web structure. Our results revealed a strong spatial coupling between community composition and food web structure along a south-north gradient. However, the temporal covariation between community composition and food web structure depended on the spatial scale. We observed a temporal mismatch at regional scale, but a strong coupling at local scale. In particular, we found that community composition can be influenced by hydro-climatic events over large areas, with diverse effects manifesting in local food web structure. Our proposed methodological framework quantified and compared spatio-temporal changes in community composition and food web structure, providing key information to support effective management strategies aimed at conserving the structure and functioning of ecological communities in times of environmental change.
  • Santos, Micaela; Cagnolo, Luciano; Roslin, Tomas; Ruperto, Emmanuel; Bernaschini, María Laura; Vázquez, Diego (2021)
    Studying how habitat loss affects the tolerance of ecological networks to species extinction (i.e. their robustness) is key for our understanding of the influence of human activities on natural ecosystems. With networks typically occurring as local interaction networks interconnected in space (a meta-network), we may ask how the loss of specific habitat fragments affects the overall robustness of the meta-network. To address this question, for an empirical meta-network of plants, herbivores and natural enemies we simulated the removal of habitat fragments in increasing and decreasing order of area, age and connectivity for plant extinction and the secondary extinction of herbivores, natural enemies and their interactions. Meta-network robustness was characterized as the area under the curve of remnant species or interactions at the end of a fragment removal sequence. To pinpoint the effects of fragment area, age and connectivity, respectively, we compared the observed robustness for each removal scenario against that of a random sequence. The meta-network was more robust to the loss of old (i.e. long-fragmented), large, connected fragments than of young (i.e. recently fragmented), small, isolated fragments. Thus, young, small, isolated fragments may be particularly important to the conservation of species and interactions, while contrary to our expectations larger, more connected fragments contribute little to meta-network robustness. Our findings highlight the importance of young, small, isolated fragments as sources of species and interactions unique to the regional level. These effects may largely result from an unpaid extinction debt, whereby younger fragments are likely to lose species over time. Yet, there may also be more long-lasting effects from cultivated lands (e.g. water, fertilizers and restricted cattle grazing) and network complexity in small, isolated fragments. Such fragments may sustain important biological diversity in fragmented landscapes, but maintaining their conservation value may depend on adequate restoration strategies.
  • McLeod, Anne; Leroux, Shawn J.; Gravel, Dominique; Chu, Cindy; Cirtwill, Alyssa R.; Fortin, Marie-Josee; Galiana, Nuria; Poisot, Timothee; Wood, Spencer A. (2021)
    Collecting well-resolved empirical trophic networks requires significant time, money and expertise, yet we are still lacking knowledge on how sampling effort and bias impact the estimation of network structure. Filling this gap is a critical first step towards creating accurate representations of ecological networks and for teasing apart the impact of sampling compared to ecological and evolutionary processes that are known to create spatio-temporal variation in network structure. We use a well-sampled spatial dataset of lake food webs to examine how sample effort influences network structure. Specifically, we predict asymptotic network properties (ANPs) for our dataset by comparing lake-specific network metrics with increasing sampling effort. We then contrast three sampling strategies - random, smallest lake to largest lake or largest lake to smallest lake - to assess which strategy best captures the regional metaweb (i.e. network of all potential interactions) network properties. We demonstrate metric-specific relationships between sample effort and network metrics, often diverging from the ANPs. For example, low sample effort can contribute to much lower and poorer estimates of closeness centralization, as compared to approximations of modularity with similar sample efforts. In fact, many network metrics (e.g. connectance) have a quadratic relationship with sample effort indicating a sampling 'sweet spot', which represents optimal sample effort for a close approximation of the ANP. Further, we find that sampling larger lakes followed by smaller lakes is a more optimal sampling strategy for capturing metaweb properties in this lentic ecosystem. Overall, we provide clear ways to better understand the impacts of sampling bias in food-web studies which may be particularly critical given the rapid increase in studies comparing food webs across space and time.
  • Kaunisto, Kari M; Roslin, Tomas; Forbes, Mark; Morrill, Andre; Sääksjärvi, Ilari Eerikki; Puisto, Anna; Lilley, Thomas; Vesterinen, Eero (2020)
    To understand the diversity and strength of predation in natural communities, researchers must quantify the total amount of prey species in the diet of predators. Metabarcoding approaches have allowed widespread characterization of predator diets with high taxonomic resolution. To determine the wider impacts of predators, researchers should combine DNA techniques with estimates of population size of predators using mark–release–recapture (MRR) methods, and with accurate metrics of food consumption by individuals. Herein, we estimate the scale of predation exerted by four damselfly species on diverse prey taxa within a well‐defined 12‐ha study area, resolving the prey species of individual damselflies, to what extent the diets of predatory species overlap, and which fraction of the main prey populations are consumed. We identify the taxonomic composition of diets using DNA metabarcoding and quantify damselfly population sizes by MRR. We also use predator‐specific estimates of consumption rates, and independent data on prey emergence rates to estimate the collective predation pressure summed over all prey taxa and specific to their main prey (non‐biting midges or chironomids) of the four damselfly species. The four damselfly species collectively consumed a prey mass equivalent to roughly 870 (95% CL 410–1,800) g, over 2 months. Each individual consumed 29%–66% (95% CL 9.4–123) of its body weight during its relatively short life span (2.1–4.7 days; 95% CL 0.74–7.9) in the focal population. This predation pressure was widely distributed across the local invertebrate prey community, including 4 classes, 19 orders and c. 140 genera. Different predator species showed extensive overlap in diets, with an average of 30% of prey shared by at least two predator species. Of the available prey individuals in the widely consumed family Chironomidae, only a relatively small proportion (0.76%; 95% CL 0.35%–1.61%) were consumed. Our synthesis of population sizes, per‐capita consumption rates and taxonomic distribution of diets identifies damselflies as a comparatively minor predator group of aerial insects. As the next step, we should add estimates of predation by larger odonate species, and experimental removal of odonates, thereby establishing the full impact of odonate predation on prey communities.