Phylogenetic trait‐based analyses of ecological networks

Abstract

Ecological networks of two interacting guilds of species, such as flowering plants and pollinators, are common in nature, and studying their structure can yield insights into their resilience to environmental disturbances. Here we develop analytical methods for exploring the strengths of interactions within bipartite networks consisting of two guilds of phylogenetically related species. We then apply these methods to investigate the resilience of a plant–pollinator community to anticipated climate change. The methods allow the statistical assessment of, for example, whether closely related pollinators are more likely to visit plants with similar relative frequencies, and whether closely related pollinators tend to visit closely related plants. The methods can also incorporate trait information, allowing us to identify which plant traits are likely responsible for attracting different pollinators. These questions are important for our study of 14 prairie plants and their 22 insect pollinators. Over the last 70 years, six of the plants have advanced their flowering, while eight have not. When we experimentally forced earlier flowering times, five of the six advanced-flowering species experienced higher pollinator visitation rates, whereas only one of the eight other species had more visits; this network thus appears resilient to climate change, because those species with advanced flowering have ample pollinators earlier in the season. Using the methods developed here, we show that advanced-flowering plants did not have a distinct pollinator community from the other eight species. Furthermore, pollinator phylogeny did not explain pollinator community composition; closely related pollinators were not more likely to visit the same plant species. However, differences among pollinator communities visiting different plants were explained by plant height, floral color, and symmetry. As a result, closely related plants attracted similar numbers of pollinators. By parsing out characteristics that explain why plants share pollinators, we can identify plant species that likely share a common fate in a changing climate.

The use of DNA barcodes in food web construction—terrestrial and aquatic ecologists unite!

“…By comparing food web structure to phylogenetic signal, we may explore how interacting species coevolve (Nyman et al 2007(Nyman et al , 2015Vazquez et al 2009;Rafferty and Ives 2013;Fontaine and Thébault 2015). As another line of investigation, comparisons of food webs along sites of different glacial or geological history will help us understand the rules for how communities disassemble and reassemble over time (Stone et al 2012).…”

“…Aggregating units of observation for subsequent analysis is easy, whereas disaggregating them is often impossible". In some cases, we should also be particularly determined in aiming for the highest end of resolution: in particular when asking questions on population-level dynamics, including the potential for indirect interactions such as apparent competition or apparent mutualism (Müller et al 1999;Morris et al 2004Morris et al , 2005van Veen et al 2006;Tack et al 2011), or questions on coevolution and phylogenetic structuring (Nyman et al 2007(Nyman et al , 2015Vazquez et al 2009;Rafferty and Ives 2013;Fontaine and Thébault 2015). Composite taxa may not share the same population dynamics, let alone the same evolutionary trajectories.…”

The cascading impacts of livestock grazing in upland ecosystems: a 10‐year experiment

“…Thus the mechanisms operating at our temperate grassland study site (which historically would have been forest) are likely to be different than in other ecosystems. To better understand food-web dynamics and co-evolutionary interactions, we recommend phylogenetic trait-based analyses of ecological networks (Rafferty and Ives 2013) and how these respond to livestock grazing.…”

How plants connect pollination and herbivory networks and their contribution to community stability

“…We expected that plants that share the same pollinators would share the same herbivores because in both plant-herbivore and plant-pollinator networks, it has been shown that closely related plant species are more likely to share the same herbivore species Godfray 2006, Elias et al 2013) and pollinator species (Rezende et al 2007, Rafferty andIves 2013). However, interestingly we did not find such a pattern in the network considered here and further analyses showed that there was no significant phylogenetic signal in the pollination network or in the herbivory network (see Appendix S3).…”

“…Our hypotheses were that plants that are generalists in the pollination networks are also generalists in the herbivory networks, because animals may respond similarly to plant signals (e.g., Strauss et al 2002, Adler and Bronstein 2004, Theis 2006). In addition, we expected that plants that share the same pollinators might share the same herbivores, since interaction conservatism of plants has been found in both pollination and herbivory networks, meaning that phylogenetically related plants tend to share the same interaction partners (Ives and Godfray 2006, Rezende et al 2007, Elias et al 2013, Rafferty and Ives 2013. Finally, the way plants connect pollination and herbivory networks should affect the spread of perturbations from one network to the other (Fontaine et al 2011).…”