Complexity in quantitative food webs

Banašek‐Richter, Carolin; Bersier, Louis‐Félix; Cattin, Marie-France; Baltensperger, Richard; Gabriel, Jean-Pierre; Merz, Yves; Ulanowicz, Robert E.; Tavares, Annette F.; Williams, D. Dudley; Ruiter, Peter C. de; Winemiller, Kirk O.; Naisbit, Russell E.

doi:10.1890/08-2207.1

Cited by 104 publications

(93 citation statements)

References 47 publications

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“…Studies that use weighted food web measures focussed mainly on the weighted link density, which is the number of links per species, taking link weights into account (Ulanowicz 1997;Bersier et al 2002;Banasek-Richter et al 2009). Using this measure, Ulanowicz (1997Ulanowicz ( , 2002 proposed a weighted equivalent to the complexity-stability criterion of May (1972).…”

Section: Introductionmentioning

confidence: 99%

Food web stability and weighted connectance: the complexity-stability debate revisited

2016

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How the complexity of food webs relates to stability has been a subject of many studies. Often, unweighted connectance is used to express complexity. Unweighted connectance is measured as the proportion of realized links in the network. Weighted connectance, on the other hand, takes link weights (fluxes or feeding rates) into account and captures the shape of the flux distribution. Here, we used weighted connectance to revisit the relation between complexity and stability. We used 15 real soil food webs and determined the feeding rates and the interaction strength matrices. We calculated both versions of connectance, and related these structural properties to food web stability. We also determined the skewness of both flux and interaction strength distributions with the Gini coefficient. We found no relation between unweighted connectance and food web stability, but weighted connectance was positively correlated with stability. This finding challenges the notion that complexity may constrain stability, and supports the 'complexity begets stability' notion. The positive correlation between weighted connectance and stability implies that the more evenly flux rates were distributed over links, the more stable the webs were. This was confirmed by the Gini coefficients of both fluxes and interaction strengths. However, the most even distributions of this dataset still were strongly skewed towards small fluxes or weak interaction strengths. Thus, incorporating these distribution with many weak links via weighted instead of unweighted food web measures can shed new light on classical theories.

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Section: Introductionmentioning

confidence: 99%

Food web stability and weighted connectance: the complexity-stability debate revisited

2016

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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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“…Connectance was central to the initial "complexity begets stability" debate (May, 1973(May, , 1999Pimm, 1984) and despite considerable criticism, continues to be broadly used as a measure of community complexity (Banasek-Richter et al, 2009;Gilbert, 2009;Tylianakis et al, 2010 of connectance: its calculation is debatable (Cohen et al, 1993) and it is dependent on network size, sampling effort, and to the inclusion of interaction strengths (Banasek-Richter et al, 2004;Blüthgen et al, 2008), However, connectance remains the main measure of network complexity (e.g. Banasek-Richter et al, 2009;Estrada, 2007). One of the broadly accepted generalizations involving connectance is that high connectance is a characteristic of pristine or near pristine communities that tends to protects them from secondary extinctions (Dunne et al, 2002;Thébault and Fontaine, 2010).…”

Section: Introductionmentioning

confidence: 99%

Connectance of species interaction networks and conservation value: Is it any good to be well connected?

Heleno

Devoto

Pocock

2012

Ecological Indicators

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a b s t r a c tRecently, the focus of conservation efforts gradually changed from a species-centred approach to a broader ambition of conserving functional ecosystems. This new approach relies on the understanding that much ecosystem function is a result of the interaction of species to form complex interaction networks. Therefore measures summarising holistic attributes of such ecological networks have the potential to provide useful indicators to guide and assess conservation objectives. The most generally accepted insight is that complexity in species interactions, measured by network connectance, is an important attribute of healthy communities which usually protects them from secondary extinctions. An implicit and overlooked corollary to this generalization is that conservation efforts should be directed to conserve highly connected communities. We conducted a literature review to search for empirical evidence of a relationship between connectance (complexity) and conservation value (communities on different stages of degradation). Our results show that the often assumed positive relationship between highly connected and desirable (i.e. with high conservation value) communities does not derive from empirical data and that the topic deserves further discussion. Given the conflicting empirical evidence revealed in this study, it is clear that connectance on its own cannot provide clear information about conservation value. In the face of the ongoing biodiversity crisis, studies of species interaction networks should incorporate the different 'conservation value' of nodes (i.e. species) in a network if it is to be of practical use in guiding and evaluating conservation practice.

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Complexity in quantitative food webs

Cited by 104 publications

References 47 publications

Food web stability and weighted connectance: the complexity-stability debate revisited

Food web stability and weighted connectance: the complexity-stability debate revisited

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

Connectance of species interaction networks and conservation value: Is it any good to be well connected?

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