Is there anybody out there? Occupancy of the carnivore guild in a temperate archipelago

Abstract

Carnivores are important components of ecological communities with wide-ranging effects that vary with carnivore size, natural history, and hunting tactics. Researchers and managers should strive to understand both the presence and distribution of carnivores within their local environment. We studied the carnivore guild in the Apostle Islands, w h e r e the distribution and occupancy of carnivores was largely unknown. We monitored 19 islands with 160 functioning camera traps from 2014-2017, from which we collected 203,385 photographs across 49,280 trap nights. We documented 7,291 total wildlife events with 1,970 carnivore events, and detected 10 of the 12 terrestrial carnivores found in Wisconsin. Detection rates for species were generally higher in summer than winter, except for coyotes (Canis latrans) and red foxes (Vulpes vulpes). Finitesample occupancy estimates for carnivores varied across islands, with mean estimated occupancy across islands varying from a high of 0.73 for black bears to a low of 0.21 for gray wolves. Of the potential island biogeography explanatory variables for carnivore occupancy we considered, island size was the most important, followed by distance to the mainland, and then interisland distance. We estimated that terrestrial carnivore species varied in the number of islands they were detected on from 1 island for gray wolves to 13 islands for black bears. Estimated carnivore richness across islands (i.e., the number of carnivores occupying an island) also varied substantively from 1 species on Michigan Island to 10 species on Stockton Island. Island size and connectivity between islands appear important for the persistence of the carnivore community in the Apostle Islands. Nomenclature: List of Mammals (2018).

Resource limitations and competitive interactions affect carnivore community composition at different ecological scales in a temperate island system

“…Microclimatic conditions and vegetative communities are variable between islands depending on the island size, elevation and location within Lake Superior (Judziewicz and Koch 1993; Supplementary material 1). The average temperature for the duration of this study was 4.4°C, with minimum and maximum temperatures ranging from −30.0°C to 32.8°C, and mean annual precipitation was 82.8 cm of rainfall and 197.4 cm of snowfall (Allen et al 2018a). Ice cover in the Bayfield harbor, which is indicative of overall lake trends, has decreased about 3 days/decade over the past 150 years (Howk 2009), and the ice season has begun an average of 11.7 days later and ended 3.0 days earlier every decade since 1975 (Howk 2009).…”

A recovery network leads to the natural recolonization of an archipelago and a potential trailing edge refuge

“…The naı ¨ve densities of martens on the islands are high (0.42-1.46 km −2 ), especially compared to recent estimates on the mainland of Wisconsin (<0.08 km −2 [Manlick et al 2016, Grauer et al 2019) and are comparable to density estimates generated from locations featuring highquality habitat and high prey densities (Francis and Stephenson 1972, Soutiere 1979, Thompson and Colgan 1994. High densities of martens on the Apostle Islands are likely a combination of reduced competition with other carnivores (Allen et al 2018) and high-quality habitat potentially featuring greater abundance of preferred prey items. On the mainland, marten populations could be limited in part by preferred prey availability; instead they are reliant on shrews (Blarina brevicauda, Sorex spp.)…”

“…High densities of martens on the Apostle Islands are likely a combination of reduced competition with other carnivores (Allen et al. 2018) and high‐quality habitat potentially featuring greater abundance of preferred prey items. On the mainland, marten populations could be limited in part by preferred prey availability; instead they are reliant on shrews ( Blarina brevicauda , Sorex spp.)…”

“…Unexpectedly, a marten was observed in 2014 on an Apostle Island, motivating research that has uncovered past photographic records dating martens back to 2010. To date, martens have been detected on 8 of 22 islands (Allen et al 2018).…”

Insectivorous bat occupancy is mediated by drought and agricultural land use in a highly modified ecoregion

“…This latent variable (w in below model) has a specified prior of B e rnoulli (0.5). We investigated covariates when the indicator variable posterior mean was included in 50% or more iterations (greater than 0.5) (Allen et al., 2018; Whitlock et al., 2020). Covariates with an indicator variable value between 0.5 and 0.9 had substantial uncertainty, with 90% credible intervals overlapping zero.…”