Three-dimensional partitioning of resources by congeneric forest predators with recent sympatry

Abstract

Coexistence of ecologically similar species can be maintained by partitioning along one or more niche axes. Three-dimensional structural complexity is central to facilitating resource partitioning between many forest species, but is underrepresented in field-based studies. We examined resource selection by sympatric northern spotted owls ( Strix occidentalis caurina ), a threatened species under the US Endangered Species Act, and nonnative barred owls ( S . varia ) in western Oregon, USA to explore the relative importance of canopy heterogeneity, vertical complexity of forest, and abiotic features to resource selection and identify potential differences that may facilitate long-term coexistence. We predicted that within home range selection of understory densities, measured with airborne lidar, would differ between species based on proportional differences in arboreal and terrestrial prey taken by each owl species. We used discrete choice models and telemetry data from 41 spotted owls and 38 barred owls monitored during 2007–2009 and 2012–2015. Our results suggested that while both species used tall canopy areas more often than low canopy areas, spotted owls were more commonly found in areas with lower tree cover, more developed understory, and steeper slopes. This is the first evidence of fine-scale partitioning based on structural forest properties by northern spotted owls and barred owls.

Review of the effects of barred owls on spotted owls

“…By contrast, Jenkins et al () reported that barred owls in the breeding season selected areas with low coverage of understory vegetation 4–8 m tall, whereas spotted owls were more likely to select areas with higher coverage of that vegetation type; however, in the non‐breeding season in areas of tall canopy (17.3 m), both spotted and barred owls selected areas with higher amounts of understory vegetation 4–8 m tall. This would support the hypothesis that spotted owls regularly select habitat with denser vegetation compared to barred owls, at least during the breeding season.…”

“…With the start of an experimental 5‐year plan to lethally remove barred owls from demographic study areas (Diller et al , ; Wiens et al , Wiens et al, ), there is evidence that removals can increase population growth of spotted owls in at least some areas. As noted earlier, evidence also suggests that quality habitat may buffer spotted owls from the negative influences of barred owls (Dugger et al ) and that spotted owls may have slight differences in use of forests and terrain, such as denser understory and steeper terrains, to carve out refugia (Jenkins et al ). Thus, strategic removals coupled with management prescriptions that promote quality spotted owl habitat may represent the 2‐pronged strategy necessary to save the species, or at least slow population decline until new alternatives can be identified.…”

“…In a recent study, Jenkins et al () employed light detection and ranging (LIDAR) data to examine vegetation structure used by spotted and barred owls in Oregon's Coast Range and observed that the 2 species may select slightly different habitats. They reported spotted owls selected forests with less canopy cover where trees were tall (>10 m), whereas barred owls were more associated with higher canopy cover regardless of tree height.…”

A Convolutional Neural Network and R-Shiny App for Automated Identification and Classification of Animal Sounds

“…As detailed in Ruff et al (2020), the project derived from ongoing monitoring efforts for the northern spotted owl (Strix occidentalis caurina), which is an important conservation and management species in the Pacific Northwest, USA, and is facing declining populations and various threats to persistence , Jenkins et al 2019.…”

Competition and Intraguild Predation Between Beetles, Pterostichus stygicus (Coleoptera: Carabidae) and Centipedes, Scolopocryptops sexspinosus (Scolopemdromorpha: Scolopocryptopidae)

“…Competition for resources among species is thought to be ecologically important and can influence community structure and stability (Niemelä 1993, Levine et al 2017, but see Lövei and Sunderland 1996). At the community level, interspecific competition can lead to coexistence via niche partitioning, competitive exclusion, or local extinction of the inferior competitor (Schoener 1974, Jenkins et al 2019. Although there is empirical evidence of strong competitive interactions between phylogenetically distinct species, many studies have focused on testing the competition-relatedness hypothesis (Darwin and Wallace 1858) which predicts that niche space overlap, and therefore competition, should be greatest between closely related species because of morphological and functional similarity (i.e., niche conservatism).…”