Sampling effects and the robustness of quantitative and qualitative food-web descriptors

Banašek‐Richter, Carolin; Cattin, Marie-France; Bersier, Louis‐Félix

doi:10.1016/s0022-5193(03)00305-9

Cited by 118 publications

(113 citation statements)

References 45 publications

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“…The importance of network dimensions was previously documented for dependence asymmetry and connectance by Olesen and co-workers (2002; and Blüthgen et al (2007), who also showed that the H 2 '-index was robust. For sampling intensity, and thus realized number of links, our results are concordant with the findings of Banasek-Richter et al (2004) and Nielsen and Bascompte (2007), who report on moderate to strong effects. Blüthgen et al (2006) report on strong effects of the number of interactions on connectance, while their proposed H 2 ' was unaffected.…”

Section: Sensitivity Of Bipartite Network Indices To Network Dimensiosupporting

confidence: 91%

Indices, Graphs and Null Models: Analyzing Bipartite Ecological Networks

Dormann¹,

Fründ²,

Blüthgen³

et al. 2009

TOECOLJ

1,469

1,542

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Many analyses of ecological networks in recent years have introduced new indices to describe network properties. As a consequence, tens of indices are available to address similar questions, differing in specific detail, sensitivity in detecting the property in question, and robustness with respect to network size and sampling intensity. Furthermore, some indices merely reflect the number of species participating in a network, but not their interrelationship, requiring a null model approach. Here we introduce a new, free software calculating a large spectrum of network indices, visualizing bipartite networks and generating null models. We use this tool to explore the sensitivity of 26 network indices to network dimensions, sampling intensity and singleton observations. Based on observed data, we investigate the interrelationship of these indices, and show that they are highly correlated, and heavily influenced by network dimensions and connectance. Finally, we re-evaluate five common hypotheses about network properties, comparing 19 pollination networks with three differently complex null models: 1. The number of links per species ("degree") follow (truncated) power law distributions. 2. Generalist pollinators interact with specialist plants, and vice versa (dependence asymmetry). 3. Ecological networks are nested. 4. Pollinators display complementarity, owing to specialization within the network. 5. Plant-pollinator networks are more robust to extinction than random networks. Our results indicate that while some hypotheses hold up against our null models, others are to a large extent understandable on the basis of network size, rather than ecological interrelationships. In particular, null model pattern of dependence asymmetry and robustness to extinction are opposite to what current network paradigms suggest. Our analysis, and the tools we provide, enables ecologists to readily contrast their findings with null model expectations for many different questions, thus separating statistical inevitability from ecological process.

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Section: Sensitivity Of Bipartite Network Indices To Network Dimensiosupporting

confidence: 91%

Indices, Graphs and Null Models: Analyzing Bipartite Ecological Networks

Dormann¹,

Fründ²,

Blüthgen³

et al. 2009

TOECOLJ

1,469

1,542

View full text Add to dashboard Cite

show abstract

“…Most network structure descriptors are affected by sampling effort to some degree (Blüthgen 2010;Blüthgen, Fründ, Vázquez, & Menzel 2008;Rivera-Hutinel, Bustamante, Marín, & Medel 2012), with qualitative indices being more sensitive to sample size than quantitative analogues (Banasek-Richter, Cattin, & Bersier 2004). Specifically, poor sampling underestimates the real diversity of links, truncating estimated trophic breath and leading to a biased network structure (Blüthgen et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Sampling completeness in seed dispersal networks: When enough is enough

Costa

Silva

Ramos

et al. 2016

Basic and Applied Ecology

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Ecological networks are an increasingly popular tool to explore community assembly rules and frame practical conservation issues. However, most described networks vary largely in sampling effort, hampering the distinction of true biological patterns from artefacts caused by poor sampling. Identifying entire seeds in the droppings of mist-netted birds is generally considered a preferred sampling method for building unbiased, quantitative seed dispersal networks. We retrieved seeds from the droppings of 936 mist-netted birds captured during five days in seven sites in Portugal and estimated sampling completeness as the diversity of seed species, disperser species, and links detected with respect to those predicted by Chao 2 estimator. In one of those sites, sampling effort was extended to 25 days to evaluate the sensitivity of ten network structure descriptors to increasing sampling effort. After five sampling days we detected 93% of the seed species, 97% of the disperser species, and 79% of the links predicted by Chao 2, however sampling for 25 days resulted in the detection of more seeds, dispersers, and links than those estimated at day 5. Most network descriptors only began to stabilize around day 8, except for Connectance and Weighted Connectance that stabilized earlier. Similarly, only after 8 days most networks descriptors significantly departed from the confidence interval estimated by null models exclusively constrained by species abundances, thus reflecting independent ecological patterns. Nestedness was the only exception, as it never departed from the null models. We suggest that Chao 2 may slightly underestimate the real diversity and that in our case at least eight sampling days were needed to build a sound seed dispersal network as 67% of the seeds, 88% of the dispersers, and 71% of the links were detected. Our results have important implications for the interpretation of seed dispersal networks because under-sampled networks may produce biased descriptors that do not suitably characterize the focal communities. ZusammenfassungÖkologische Netzwerke werden immer beliebter als eine Methode, um die 'assembly rules' für Gemeinschaften zu untersuchen und praktische Naturschutzregeln zu entwerfen.

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“…We used recently developed quantitative, weighted descriptors of food web complexity [28] that are more accurate, more robust to differences in sampling effort and less sensitive to among system differences, compared with their qualitative counterparts [29,30]. They account for variation in link magnitude and energetic importance of each species in a community.…”

Section: Introductionmentioning

confidence: 99%

Food web structure and biocontrol in a four-trophic level system across a landscape complexity gradient

et al. 2011

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Decline in landscape complexity owing to agricultural intensification may affect biodiversity, food web complexity and associated ecological processes such as biological control, but such relationships are poorly understood. Here, we analysed food webs of cereal aphids, their primary parasitoids and hyperparasitoids in 18 agricultural landscapes differing in structural complexity (42 -93% arable land). Despite little variation in the richness of each trophic group, we found considerable changes in trophic link properties across the landscape complexity gradient. Unexpectedly, aphid -parasitoid food webs exhibited a lower complexity (lower linkage density, interaction diversity and generality) in structurally complex landscapes, which was related to the dominance of one aphid species in complex landscapes. Nevertheless, primary parasitism, as well as hyperparasitism, was higher in complex landscapes, with primary parasitism reaching levels for potentially successful biological control. In conclusion, landscape complexity appeared to foster higher parasitism rates, but simpler food webs, thereby casting doubt on the general importance of food web complexity for ecosystem functioning.

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Sampling effects and the robustness of quantitative and qualitative food-web descriptors

Cited by 118 publications

References 45 publications

Indices, Graphs and Null Models: Analyzing Bipartite Ecological Networks

Indices, Graphs and Null Models: Analyzing Bipartite Ecological Networks

Sampling completeness in seed dispersal networks: When enough is enough

Food web structure and biocontrol in a four-trophic level system across a landscape complexity gradient

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