Bringing the Eltonian niche into functional diversity

Abstract

Studies of functional diversity (FD) have gained immense interest because they promise a more mechanistic understanding of the relationship between diversity and ecosystem functioning. However, the concept of FD is currently not used to its full potential because of several biases and shortcomings. For instance, while the analysis of traits related to species’ Grinnellian niches, i.e. traits influencing species’ fitness under different environmental conditions, is well‐advanced, there is a lack of studies on the functional diversity related to species’ Eltonian niches, i.e. species’ functional roles in ecological processes and their effects on other species, a discrepancy known as the Eltonian Shortfall. Most importantly, the current indirect approach of measuring FD via species traits restricts analyses to species with similar traits, usually a taxon. Consequently, FD is generally measured for only one taxon but across different ecological processes, when it would ideally be measured for one ecological process but across all taxa that contribute to that process. These discrepancies hinder advances of our understanding of the relationship between diversity and ecosystem functions and services. We introduce a new approach to measuring functional diversity that is designed to overcome these shortcomings by bridging research on networks, species niches, and functional traits. Instead of characterizing functional roles indirectly via species’ traits, we propose to characterize functional roles directly via the traits of species’ resources and interaction partners in a given ecological process. Critically, this shift in perspective for the first time allows comparisons of the functional roles of all taxa that participate in an ecological process regardless of their own morphology. We illustrate our new approach with a study on functional roles of frugivores in seed‐dispersal systems. Our approach is an important addition to existing approaches to studying FD, and it facilitates new studies in a vastly unexplored field of functional diversity research.

Global trade‐offs of functional redundancy and functional dispersion for birds and mammals

“…We find overlap in the roles played by birds and mammals, even when including flight ability and diel activity (two major differentiators between birds and mammals), indicating cases where birds and mammals have converged on similar ecological strategies. Thus, single‐taxon analyses testing for functional redundancy and functional dispersion offer limited insights, because an unknown number of roles fulfilled by other taxa is ignored (Dehling & Stouffer, ). These results therefore demonstrate the importance of considering ecological comparability between birds and mammals in conservation strategies.…”

“…To date, functional metrics have generally been applied to single taxonomic groups at a time in terrestrial systems, despite the fact that different taxa can potentially fulfil similar and/or complementary ecological and functional roles (Dehling & Stouffer, ). Here, we recognize that birds and mammals, as mobile consumers, have the potential to be comparable ecologically, especially at broad scales and across generalizable traits, comparable to how taxonomically and ecologically diverse plants, such as large trees and small grasses, have previously been analysed together (e.g., Díaz et al, ).…”

“…To date, functional metrics have generally been applied to single taxonomic groups at a time in terrestrial systems, despite the fact that different taxa can potentially fulfil similar and/or complementary ecological and functional roles (Dehling & Stouffer, 2018).…”

Similar composition of functional roles in Andean seed‐dispersal networks, despite high species and interaction turnover

“…Comparisons of species' functional roles between species communities have been limited by the lack of suitable methods (Poisot et al 2012, Carstensen et al 2016, Dehling and Stouffer 2018, Pellisier et al 2018). Approaches to describing species' functional roles in ecological processes have so far focused on analyzing either species' functional traits or patterns of species interactions in ecological networks.…”

Resource‐use dynamics of co‐occurring chondrichthyans from the First Coast, North Florida, USA

“…Understanding the resource-use dynamics of higher predators can provide important insight into their functional role and broader processes that ultimately dictate the distribution of species in space and time (Dehling and Stouffer, 2018;Soberón 2007). This is because resource-use characteristics are capable of structuring ecological communities through mechanisms such as the regulation of prey populations (i.e., direct foraging and risk effects, Heithaus et al, 2008;Roff et al, 2016), promoting ecosystem/food-web connectivity (Doughty et al, 2015;McCauley et al, 2012;Shipley et al, 2019) and engineering habitats (Hammerschlag, 2019;O'Shea et al, 2012).…”