Functional compensation by insular scavengers: the relative contributions of vertebrates and invertebrates vary among islands

Abstract

When the extinction of some species results in loss of ecosystem functions, other species may be able to compensate for this loss. Functional compensation has recently been observed on islands where species are likely to become extinct; however, few studies have analysed functional compensation by scavengers in insular environments. Here, we investigated the ecosystem functions of vertebrate and invertebrate scavengers on Honshu, the main island of Japan, and offshore islands (four of the Oki Islands). The Oki Islands lack several native vertebrate scavengers (raccoon dogs, boars, martens, and foxes) that are abundant on Honshu. We experimentally placed mouse carcasses on the forest floors of Honshu (12 sites) and the Oki Islands (7 sites on Dōgo, 4 sites on Nishinoshima, 4 sites on Nakanoshima, and 3 sites on Chiburijima) in September–October 2014 and 2015. Nearly all of the mouse carcasses (95–100%) placed on the forest floor disappeared within 1 week. However, the relative importance of vertebrate and invertebrate scavengers varied among islands. Vertebrate and invertebrate scavengers contributed equally on Honshu (carcass removal by vertebrates, 47%), whereas vertebrate scavengers rarely contributed to carcass removal on three of the Oki Islands (carcass removal by vertebrates: 17% on Dōgo, 30% on Nishinoshima, and 5% on Nakanoshima). Consequently, invertebrate scavengers (Nicrophorus burying beetles) functionally compensated for the low species diversity of vertebrate scavengers on the three islands (carcass burial by Nicrophorus beetles, 65–95%). However, on the small island of Chiburijima, introduced raccoon dogs contributed to nearly all of the removals (93%), suggesting that introduced scavengers can compensate for the functional reduction. This functional compensation by scavengers may help stabilise the functions and/or services of scavengers in island environments.

Vertebrate scavenger guild composition and utilization of carrion in an East Asian temperate forest

“…This suggests that it may not have been necessary for the Japanese badger to scavenge because of the abundance of invertebrates. We also expected Japanese weasels to scavenge because of previous documentation of scavenging on mouse carcasses (Sugiura & Hayashi, ; Sugiura et al, ). However, previous diet analysis showed they feed on small vertebrates and not vertebrates that are larger than themselves (e.g., Asahi, ; Furuya, Kishida, Swnoo, Noguchi, & Yamasaki, ).…”

“…The majority of scavengers in most ecosystems are facultative rather than obligate (Wilson & Wolkovich, 2011), making it important to evaluate the complex interactions between facultative scavengers at carrion to understand their function in ecosystem dynamics (Cortés-Avizanda, Selva, Carrete, & Donázar, 2009;Sebastián-González et al, 2016;Selva & Fortuna, 2007). Nevertheless, few studies have dealt with facultative scavenging activities in the Asian temperate forest ecosystem (e.g., Sugiura, Tanaka, Taki, & Kanzaki, 2013, Sugiura & Hayashi, 2018 and there have been no studies focused on facultative scavenger guilds at large ungulate carcasses. Japan (East Asian islands, approximately 378,000 km 2 ) is designated as an ecosystem hot spot with high biodiversity (Mittermeier, Myers, Mittermeier, & Robles, 1999) and has stable forest ecosystems that provide habitat for various, densely populated species of mammals.…”

“…The majority of scavengers in most ecosystems are facultative rather than obligate (Wilson & Wolkovich, ), making it important to evaluate the complex interactions between facultative scavengers at carrion to understand their function in ecosystem dynamics (Cortés‐Avizanda, Selva, Carrete, & Donázar, ; Sebastián‐González et al, ; Selva & Fortuna, ). Nevertheless, few studies have dealt with facultative scavenging activities in the Asian temperate forest ecosystem (e.g., Sugiura, Tanaka, Taki, & Kanzaki, , Sugiura & Hayashi, ) and there have been no studies focused on facultative scavenger guilds at large ungulate carcasses.…”

The fate of small-mammal carrion is affected by carcass size and visual conspicuousness in a Neotropical rainforest

“…They may be locating these carcasses faster, detecting putrifaction cues at lower concentrations, or are simply highly abundant and able to arrive at the carcasses more quickly. While the efficiency of different scavenger guilds (vertebrates vs. beetles) can vary in different habitats, ecosystem function is typically sustained (Sugiura et al 2013;Sugiura and Hayashi 2018). Therefore, research focused on understanding how these complex interactions between invertebrate and vertebrate scavengers maintain ecosystem function would be timely to help create a more developed framework for Neotropical food webs.…”

Fine spatial-scale variation in scavenger activity influences avian mortality assessments on a boreal island

“…Given that the scavenging of carcasses can occur via removal by vertebrate scavengers or through decomposition by invertebrate scavengers and microbes [8], there may be high spatial and temporal variability in scavenging rates depending upon differences in the abundance of the species involved, the extent of competition for carcasses among these species, and seasonal variation in activity levels [9,10]. Island settings, often characterized by restricted communities and a lower diversity of vertebrate scavengers than are found in mainland settings, create further variability [11]. Other scavenger species (e.g., invertebrates) can compensate for this functional loss of vertebrate scavenger species on islands, altering the relative contributions of vertebrate and invertebrate community members to scavenging, and consequently affecting the overall scavenging rate [11].…”