Abstract
In environments where food resources are spatially variable and temporarily impoverished, consumers that encounter habitat patches with different food density should focus their foraging initially where food density is highest before they move to patches where food density is lower. Increasing missed opportunity costs should drive individuals progressively to patches with lower food density as resources in the initially high food density patches deplete. To test these expectations, we assessed the foraging decisions of two species of dasyurid marsupials (dunnarts: Sminthopsis hirtipes and S. youngsoni) during a deep drought, or bust period, in the Simpson Desert of central Australia. Dunnarts were allowed access to three patches containing different food densities using an interview chamber experiment. Both species exhibited clear preference for the high density over the lower food density patches as measured in total harvested resources. Similarly, when measuring the proportion of resources harvested within the patches, we observed a marginal preference for patches with initially high densities. Models analyzing behavioral choices at the population level found no differences in behavior between the two species, but models analyzing choices at the individual level uncovered some variation. We conclude that dunnarts can distinguish between habitat patches with different densities of food and preferentially exploit the most valuable. As our observations were made during bust conditions, experiments should be repeated during boom times to assess the foraging economics of dunnarts when environmental resources are high.
Highlights
Charles Darwin, upon reaching south western Australia, proclaimed: ‘‘. . . the soil sandy, and very poor; it supported either a coarse vegetation of thin, low brushwood and wiry grass, or a forest of stunted trees . . . [the reader] will never wish to walk again in so uninviting a country’’ (Darwin, 1839: 449–450)
The physiological adaptations of desert-dwelling mammals have been much studied (Degen et al, 1997; Geiser, 2004; Schwimmer & Haim, 2009), but the behavioral responses of these mammals to arid environments are less well known. Large species such as giraffe (Giraffa camelopardalis) can move long distances to escape regional areas stricken by harsh climatic conditions (Fennessy, 2009), whereas others retreat to localized refuges that provide secure resources and buffered microclimates (McDonald et al, 2015)
In this study we assessed the ability of two species of dunnart, captured in central Australia during a prolonged period of rainfall deficit, i.e., a ‘bust,’ to select habitat patches based on their food quality
Summary
Charles Darwin, upon reaching south western Australia, proclaimed: ‘‘. . . the soil sandy, and very poor; it supported either a coarse vegetation of thin, low brushwood and wiry grass, or a forest of stunted trees . . . [the reader] will never wish to walk again in so uninviting a country’’ (Darwin, 1839: 449–450). Had Darwin visited central Australia instead, he would have found still sandier soils and much harsher and less predictable climatic conditions, and an extraordinary diversity of small vertebrates that prevail there even during periods of severe rainfall deficit. Many of these species, notably small and medium-sized mammals (Woinarski, Burbidge & Harrison, 2014), have since declined to extinction in. In this study we assessed the ability of two species of dunnart, captured in central Australia during a prolonged period of rainfall deficit, i.e., a ‘bust,’ to select habitat patches based on their food quality. As the two species of dunnart differ in size, and probably in competitive ability (Dickman, 1991; Fisher & Dickman, 1993b), we expected the larger species to be more responsive to variation in patch quality than the smaller species; larger dunnarts should be more selective as they are accustomed to gaining priority of access at food sources, and have greater food requirements
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