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Red squirrel middens influence abundance but not diversity of other vertebrates.

Posthumus EE, Koprowski JL, Steidl RJ - PLoS ONE (2015)

Bottom Line: After accounting for local forest characteristics, however, only species richness of medium-to-large mammals was associated with a red squirrel being resident during surveys.In areas where red squirrels were resident during surveys or in areas with greater amounts of resources concentrated by red squirrels, abundances of two of four small mammal species and two of four bird species increased.We conclude that the presence of this ecosystem modifier and the resources it concentrates influence abundance of some mammals and birds, which may have implications for maintaining biodiversity across the wide geographic range inhabited by red squirrels and other larderhoarding animals.

View Article: PubMed Central - PubMed

Affiliation: Wildlife and Fisheries Science, School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona, United States of America.

ABSTRACT
Some animals modify the environment in ways that can influence the resources available to other species. Because red squirrels (Tamiasciurus hudsonicus) create large piles of conifer-cone debris (middens) in which they store cones, squirrels concentrate resources that might affect biodiversity locally. To determine whether other animals are attracted to midden sites beyond their affinity for the same resources that attract red squirrels, we assessed associations between middens, mammals, and birds at population and community levels. We surveyed 75 middens where residency rates of red squirrels varied during the previous five years; sampling along this residency gradient permitted us to evaluate the influence of resources at middens beyond the influence of a resident squirrel. At each location, we quantified vegetation, landscape structure, abundance of conifer cones, and midden structure, and used capture-recapture, distance sampling, and remote cameras to quantify presence, abundance, and species richness of mammals and birds. Red squirrels and the resources they concentrated at middens influenced mammals and birds at the population scale and to a lesser extent at the community scale. At middens with higher residency rates of red squirrels, richness of medium and large mammals increased markedly and species richness of birds increased slightly. After accounting for local forest characteristics, however, only species richness of medium-to-large mammals was associated with a red squirrel being resident during surveys. In areas where red squirrels were resident during surveys or in areas with greater amounts of resources concentrated by red squirrels, abundances of two of four small mammal species and two of four bird species increased. We conclude that the presence of this ecosystem modifier and the resources it concentrates influence abundance of some mammals and birds, which may have implications for maintaining biodiversity across the wide geographic range inhabited by red squirrels and other larderhoarding animals.

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Red squirrel (Tamiasciurus hudsonicus) midden.Photographs of (a) red squirrel (Tamiasciurus hudsonicus) midden cone-scale pile, (b) cached cones inside pit excavated by red squirrel, and (c) stored cones, which may number in the thousands at a single midden. Photo credit, E. E. Posthumus. Mt. Graham, Graham Co. Arizona, 2011–2012.
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pone.0123633.g001: Red squirrel (Tamiasciurus hudsonicus) midden.Photographs of (a) red squirrel (Tamiasciurus hudsonicus) midden cone-scale pile, (b) cached cones inside pit excavated by red squirrel, and (c) stored cones, which may number in the thousands at a single midden. Photo credit, E. E. Posthumus. Mt. Graham, Graham Co. Arizona, 2011–2012.

Mentions: Some species also alter the distribution of resources, concentrating resources for themselves and in ways that could increase the availability of resources for other species [15]. Handling and storage of food by animals for later use, termed larderhoarding, enables animals to satisfy energy requirements when resource abundance fluctuates [15]. Red squirrels (Tamiasciurus hudsonicus), a territorial tree squirrel distributed throughout most coniferous forests of the United States and Canada [16], often larderhoard food supplies that last for years [15, 17]. Red squirrels fulfill a number of important ecosystem functions, including dispersing seeds, serving as prey for predators, and creating structure via conspicuous cone-scale piles, known as middens, which are a product of feeding in a single location (Fig 1) [16]. Middens are central to a single red squirrel’s well-defended territory [16], which can vary from 1 to >10 ha [18]. In the southwestern United States, middens are typically located in forest patches with locally dense canopies, high stem densities, thick foliage, and on cooler north-facing slopes [19–20], and have a cool, moist microclimate optimal to larderhoard conifer cones and fungi [21–22]. Middens often are used over multiple generations [17] and can reach 13 m in diameter and 50 cm in depth [23]. The structure of middens facilitates tunneling, nesting, and access to thousands of stored cones, plus seeds dropped during feeding are distributed throughout a red squirrel’s territory [24]. These resources may attract small mammals and birds, which may in turn attract other predatory mammals and birds [25–26].


Red squirrel middens influence abundance but not diversity of other vertebrates.

Posthumus EE, Koprowski JL, Steidl RJ - PLoS ONE (2015)

Red squirrel (Tamiasciurus hudsonicus) midden.Photographs of (a) red squirrel (Tamiasciurus hudsonicus) midden cone-scale pile, (b) cached cones inside pit excavated by red squirrel, and (c) stored cones, which may number in the thousands at a single midden. Photo credit, E. E. Posthumus. Mt. Graham, Graham Co. Arizona, 2011–2012.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4414347&req=5

pone.0123633.g001: Red squirrel (Tamiasciurus hudsonicus) midden.Photographs of (a) red squirrel (Tamiasciurus hudsonicus) midden cone-scale pile, (b) cached cones inside pit excavated by red squirrel, and (c) stored cones, which may number in the thousands at a single midden. Photo credit, E. E. Posthumus. Mt. Graham, Graham Co. Arizona, 2011–2012.
Mentions: Some species also alter the distribution of resources, concentrating resources for themselves and in ways that could increase the availability of resources for other species [15]. Handling and storage of food by animals for later use, termed larderhoarding, enables animals to satisfy energy requirements when resource abundance fluctuates [15]. Red squirrels (Tamiasciurus hudsonicus), a territorial tree squirrel distributed throughout most coniferous forests of the United States and Canada [16], often larderhoard food supplies that last for years [15, 17]. Red squirrels fulfill a number of important ecosystem functions, including dispersing seeds, serving as prey for predators, and creating structure via conspicuous cone-scale piles, known as middens, which are a product of feeding in a single location (Fig 1) [16]. Middens are central to a single red squirrel’s well-defended territory [16], which can vary from 1 to >10 ha [18]. In the southwestern United States, middens are typically located in forest patches with locally dense canopies, high stem densities, thick foliage, and on cooler north-facing slopes [19–20], and have a cool, moist microclimate optimal to larderhoard conifer cones and fungi [21–22]. Middens often are used over multiple generations [17] and can reach 13 m in diameter and 50 cm in depth [23]. The structure of middens facilitates tunneling, nesting, and access to thousands of stored cones, plus seeds dropped during feeding are distributed throughout a red squirrel’s territory [24]. These resources may attract small mammals and birds, which may in turn attract other predatory mammals and birds [25–26].

Bottom Line: After accounting for local forest characteristics, however, only species richness of medium-to-large mammals was associated with a red squirrel being resident during surveys.In areas where red squirrels were resident during surveys or in areas with greater amounts of resources concentrated by red squirrels, abundances of two of four small mammal species and two of four bird species increased.We conclude that the presence of this ecosystem modifier and the resources it concentrates influence abundance of some mammals and birds, which may have implications for maintaining biodiversity across the wide geographic range inhabited by red squirrels and other larderhoarding animals.

View Article: PubMed Central - PubMed

Affiliation: Wildlife and Fisheries Science, School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona, United States of America.

ABSTRACT
Some animals modify the environment in ways that can influence the resources available to other species. Because red squirrels (Tamiasciurus hudsonicus) create large piles of conifer-cone debris (middens) in which they store cones, squirrels concentrate resources that might affect biodiversity locally. To determine whether other animals are attracted to midden sites beyond their affinity for the same resources that attract red squirrels, we assessed associations between middens, mammals, and birds at population and community levels. We surveyed 75 middens where residency rates of red squirrels varied during the previous five years; sampling along this residency gradient permitted us to evaluate the influence of resources at middens beyond the influence of a resident squirrel. At each location, we quantified vegetation, landscape structure, abundance of conifer cones, and midden structure, and used capture-recapture, distance sampling, and remote cameras to quantify presence, abundance, and species richness of mammals and birds. Red squirrels and the resources they concentrated at middens influenced mammals and birds at the population scale and to a lesser extent at the community scale. At middens with higher residency rates of red squirrels, richness of medium and large mammals increased markedly and species richness of birds increased slightly. After accounting for local forest characteristics, however, only species richness of medium-to-large mammals was associated with a red squirrel being resident during surveys. In areas where red squirrels were resident during surveys or in areas with greater amounts of resources concentrated by red squirrels, abundances of two of four small mammal species and two of four bird species increased. We conclude that the presence of this ecosystem modifier and the resources it concentrates influence abundance of some mammals and birds, which may have implications for maintaining biodiversity across the wide geographic range inhabited by red squirrels and other larderhoarding animals.

Show MeSH
Related in: MedlinePlus