Food webs without the food: population models for dynamic desert rivers

Authors: David Lytle, David Merritt, Jonathan Tonkin, Julian Olden, Lindsay Reynolds, Patrick Deleenheer, Laura McMullen

Year: 2017 (xlix)

Abstract

Community models fall along a spectrum of assumptions about species and their interactions At one end, neutral biodiversity models do not require information about individual species’ biology At the other end, food web models define species largely in terms of biotic interactions that may or may not be understood Interaction-neutral models present an alternative community modelling approach that falls in between Species are highly-specified by their unique vital rates (fecundity, mortality, growth rate, etc) under a range of environmental conditions, and these vital rates are incorporated into individual matrix population models or other suitable modelling structures A dependency assumption (finite space for recruitment, upper limits on aggregate biomass, etc) links individual matrices together, and cross-species sensitivity analysis can then be used to discover pairwise biotic interactions This approach is especially suitable for desert rivers and streams, where population dynamics are strongly influenced by flood, droughts, and other hydrologic dynamics We developed interaction-neutral models for riparian vegetation, aquatic invertebrates, and fish Models recovered field-observed community patterns, suggesting that abiotic forcing by floods and droughts explains a significant amount of population dynamics Cross-species sensitivity analysis identified species that had strong biotic effects on other community members (keystone species), as well as species with high bidirectional effects (mutual) or little influence on other species (passive) These results show promise for forecasting climate-induced population shifts in river ecosystems In general, interaction-neutral models could be useful for modeling communities where among-species biotic interactions are poorly understood or highly dependent on environmental context