Functional replacement across species pools of vertebrate scavengers separated at a continental scale maintains an ecosystem function

Abstract

1. The composition of species pools can vary in space and time. While many studies are focused on understanding which factors influence the make-up of species pools, the question to which degree biogeographic variation in species composition propagates to biogeographic variation in ecological function is rarely examined. If different local species assemblages operate in ways that maintain specific ecological processes across continents, they can be regarded as functionally equivalent. Alternatively, variation in species assemblages might result in the loss of ecological function if different species fulfil different functions, and thereby fail to maintain the ecological process. 2. Here, we test whether ecological function is affected by differences in the composition of species pools across a continental scale, comparing a tropical with a temperate pool. The model systems are assemblages of vertebrates foraging on ocean beaches, and the ecological function of interest is the consumption of wave-cast carrion, a pivotal process in sandy shore ecosystems. 3. We placed fish carcasses (n = 179) at the beach-dune interface, monitored by motion-triggered cameras to record scavengers and quantify the detection and removal of carrion. Scavenging function was measured on sandy beaches in two distinct biogeographic regions of Australia: tropical north Queensland and temperate Victoria. 4. The composition of scavenging assemblages on sandy beaches varied significantly across the study domain. Raptors dominated in the tropics, while invasive red foxes were prominent in temperate assemblages. Notwithstanding the significant biogeographic change in species composition, ecological function -as indexed by carcass detection and removal -was maintained, suggesting strong functional replacement at the continental scale. 5. Species pools of vertebrate scavengers that are assembled from taxonomically distinct groups (birds vs. mammals) and located in distinct climatic regions (temperate vs. tropical) can maintain an ecological process via replacement of species with comparable functional traits.

Urbanisation supplements ecosystem functioning in disturbed estuaries

“…For example, mud crabs Scylla serrata are abundant, and avid scavengers of carrion, in estuaries over the austral summer (Webley 2008). The availability of carrion to estuarine scavengers might also vary as a function of seasonality, or with changes in the extent of shoreline modification (Huijbers et al 2016). Large accumulations of animal carcasses were not observed in any of the estuaries we studied, which suggests that substantial differences in carrion availability were not a major factor in contributing to observed patterns in scavenging function.…”

“…capitalising on the regular supply of food and abundance of shelter in human modified landscapes (Aronson et al 2014, Dafforn et al 2015, Firth et al 2016, Bishop et al 2017. Species that perform important ecological processes, and which are also capable of exploiting resources in urban settings might, therefore, be important in sustaining ecological functions in disturbed ecosystems (Hobbs et al 2006, Huijbers et al 2016, Mayer-Pinto et al 2018).…”

“…multiple species perform an ecological function and differ in their sensitivity to disturbance), key ecological processes might be maintained across natural and urban landscapes by different taxa that perform the same ecological functions ( Fig. 1) (Elmqvist et al 2003, Schlaepfer et al 2011, Huijbers et al 2016. By contrast, when assemblages contain limited redundancy (i.e.…”

Low redundancy and complementarity shape ecosystem functioning in a low‐diversity ecosystem

“…Similarly, a number of other species that are opportunistic scavengers in estuaries are likely to be less abundant, target more specified types of prey/carrion or have smaller body sizes, thus potentially being out‐competed by species such as yellowfin bream. It has recently been suggested that high species dominance might be a common feature of scavenger assemblages (Inger, Per, Cox, & Gaston, ), and the function of carrion consumption appears to be contingent on a small number of common, and opportunistic, trophic generalists across a range of ecosystems, including forests, deserts and coastal dunes (DeVault et al, ; Huijbers et al, ; Mateo‐Tomás, Olea, Moleón, Selva, & Sánchez‐Zapata, ). In addition to being characteristics of successful scavengers, the behavioural traits (e.g.…”

Carcasses of invasive species are predominantly utilized by invasive scavengers in an island ecosystem

“…, Huijbers et al. ). The redistribution of energy by vertebrate scavengers, as opposed to invertebrates and decomposers, could be far more influential in ecosystem‐wide trophic interactions than is currently understood (DeVault et al.…”