Special delivery: scavengers direct seed dispersal towards ungulate carcasses

Abstract

Cadaver decomposition islands around animal carcasses can facilitate establishment of various plant life. Facultative scavengers have great potential for endozoochory, and often aggregate around carcasses. Hence, they may disperse plant seeds that they ingest across the landscape towards cadaver decomposition islands. Here, we demonstrate this novel mechanism along a gradient of wild tundra reindeer carcasses. First, we show that the spatial distribution of scavenger faeces (birds and foxes) was concentrated around carcasses. Second, faeces of the predominant scavengers (corvids) commonly contained viable seeds of crowberry, a keystone species of the alpine tundra with predominantly vegetative reproduction. We suggest that cadaver decomposition islands function as endpoints for directed endozoochory by scavengers. Such a mechanism could be especially beneficial for species that rely on small-scale disturbances in soil and vegetation, such as several Nordic berry-producing species with cryptic generative reproduction.

Reindeer carcasses provide foraging habitat for insectivorous birds of the alpine tundra

“…For example, obligate scavengers like vultures play a vital role in the redistribution of nutrients derived from carcasses (Beasley et al 2015). Furthermore, facultative scavengers can direct plant seed to carcass locations and potentially contribute to genetic diversity of plant populations (Steyaert et al 2018). Science-based arguments can then lead to more scavenger-tolerant and -benefiting legislation and regulation (Margalida et al 2012).…”

“…We opportunistically conducted surveys (n = 7, between 45 and 180 min each, totalling about 11 h) at the carcass site between 8 and 12 August 2017. Avian activity was observed but not quantified from 8-10 August, given the initial focus of the Steyaert et al (2018) study, while the total and percentage of observations were calculated for the 11 and 12 August (Table 1). Those surveys (3 h each) were conducted in the early morning (06:00-09:00), whereas the others were conducted whenever time was available during daylight hours.…”

“…The latter implies that animals disperse plant seeds through ingestion (endozoochory) in disproportionate numbers towards microsites that are ideal for germination and establishment (Wenny & Levey 1998). Such directed endozoochory towards carcasses has been shown by Steyaert et al (2018) with scavengers. Carcasses can eventually become biodiversity hotspots and facilitate interactions between species (Benbow et al 2015, Martin 2016.…”

“…During fieldwork for another study in August 2017 (Steyaert et al 2018) , i.e. one year after the mass dieoff, we made incidental observations of the foraging strategies of passerines (i.e., Meadow Pipit Anthus pratensis, Northern Wheatear Oenanthe oenanthe, Common Reed Bunting Emberiza schoeniclus, Bluethroat Luscinia svecica, and Lapland Bunting Calcarius lapponicus) feeding on insects associated with carcass decomposition (predominantly blowfly adults and their larvae Calliphoridae sp.)…”

Endozoochory by brown bears stimulates germination in bilberry

“…and thrushes (Turdus spp.) (Schaumann and Heinken 2002, Harrer and Levi 2018, Steyaert et al 2018, are common in the study area. The project annually captures about 40-60 bears and marks them with GPS collars, following a standardized protocol, which has been approved by the appropriate management agencies and ethical committees (Djuretiska nämden i Uppsala, Sweden) (Arnemo et al 2011).…”