Ecological interaction networks: prospects and pitfalls

Abstract

Abstract. Interaction networks are a tool to visualize and to study the relationships between interacting species across and within trophic levels. Recent research uncovered many properties of such networks that remained undetected in previous food web studies. These patterns could be related to evolutionary and ecological processes. The study of interaction networks promises therefore progress in the study of constraints that act on the coevolution of interacting species and on food webs. However, there are still many pitfalls associated with the statistical analysis, the properties of the metrics involved and the appropriate null model choice. Here I review the mechanisms that shape interaction matrices, the possible internal structures and their ecological interpretation, and the analytical tools to identify matrix structure. Progress in the field needs critical meta-analytical and comparative studies that indentify the best suited null models (low type I and II error probabilities and high power to disentangle statistical from ecological processes) and clarify the interdependence of different concepts and metrics associated with network approaches. It is not improbable that many patterns recently associated with ecological and evolutionary processes might turn out to be simple side effects of the sampling from the underlying metacommunity distributions.

Flower-visitor and pollen transport networks in a large city: structure and properties

“…This may indicate undersampling (emphasized by the high proportion of singletons in our study), but also that some indices are of little value in studies of ephemeral and disturbed habitats such as these. This problem of ecologically meaningful reasoning based on some network metrics has already been pointed out by several authors (Blüthgen et al 2008;Ulrich 2009;Blüthgen 2010). In our case, more coherent results were obtained using pollen data, which revealed many more interactions within the studied communities.…”

“…In such cases, pollen analyses may add a valuable perspective to our knowledge of plantanimal networks (Forup and Memmott 2005;Gibson et al 2006;Forup et al 2008;Bosch et al 2009;Alarcon 2010;Devoto et al 2011;Popic et al 2013). Also, some traditionally used metrics for studying network properties, especially connectance, are said to be strongly dependent on sampling effort (Nielsen and Bascompte 2007;Vazquez et al 2009;Blüthgen et al 2006Blüthgen et al , 2008Blüthgen 2010;Dorado et al 2011), and adequate sampling of interaction diversity is labour intensive, so networks published to date may be largely undersampled (Chacoff et al 2012) and may not necessarily be ecologically meaningful (Ulrich 2009;Blüthgen 2010). Therefore, in purely technical terms, applying pollen datasets could enhance the resolution of the results as they allow us to record ''past flower visitation'' (Forup and Memmott 2005), and hence discover some existing links that usually go undetected, compensating, in some cases, lower sampling effort (Blüthgen 2010).…”

Predicting cryptic links in host-parasite networks

“…Togetherness measures the tendency of host species to share parasites, with large values suggesting ecological similarity between hosts may be more important than competition in driving community structure, and small values suggesting the opposite ([ 12 , 50 ]). The variance-to-mean ratio is an index of aggregation traditionally used in studies of single species parasite distributions [ 46 , 51 ], where larger values indicate more skewed or aggregated parasite burdens.…”

“…Recently, authors have applied concepts and tools from community ecology and graph theory to host-parasite interactions [ 4 – 7 ] in an effort to understand how host and parasite communities interact, including investigations into how host community diversity influences disease transmission [ 8 ], how parasites interact within infected hosts [ 9 ], and how host functional and phylogenetic similarity promote parasite sharing [ 10 , 11 ]. Additional research has focused on topological measures of host-parasite networks—such as nestedness [ 12 ] and modularity [ 13 ]—which attempt to quantify the formation of patterns of interactions between host and parasite species. These patterns may influence network stability [ 2 ] and resilience [ 3 ].…”

Analyzing Ecological Systems Using Network Analysis

“…Previous papers in this journal have addressed the network issue, but from a connectivity perspective (Ulrich 2009) or from an information theory perspective (Ulanowicz 2004). Other approaches to ecological network analysis have been published elsewhere such as investigation of food webs (Dunne et al 2002(Dunne et al , 2004Christian & Luczkovich 1999), pollination networks (Bascompte et al 2003;Olesen et al 2007), and keystone species (Jordan 2009;Jordan et al 2009;Ortiz et al 2013) to mention a few.…”