Role of Biotic Interactions in a Small Mammal Assemblage in Semiarid Chile

Abstract

The role of biotic interactions including vertebrate predation and interspecific competition was studied among members of a semiarid small mammal assemblage in a long-term field manipulation in north central Chile. Fences and netting selectively excluded mammalian and avian predators, and a putative rodent competitor, the degu ( Octodon de gus), from large, replicated grids. Small mammal populations were censused monthly over >4 yr, and effects of predator and degu exclusions on numbers and survival of small mammals were assessed with repeated measures ANOVAs. Marginally significant predator exclusion effects were detected on 0. degus, and highly significant year X predation interactions in both wet and dry seasons; degu survival (= persistence) was also significantly longer on exclusion grids. Predation had significant effects on numbers of Phyllotis darwini, and a significant month X predator interaction existed in the wet season; survival was also significantly higher on predator exclusion grids. There was a marginally significant year X competitor interaction in the dry season for this species. Akodon olivaceus had significant month X predator and month X competitor interactions in the wet season only; survival was significantly longer on degu exclusion grids. An irruptive species, Oligoryzomys longicaudatus, showed no significant predator or competitor effects in 1991-1992; however, survival was significantly longer on predator + competitor exclusion (vs. control) grids.An uncommon species, Abrothrix longipilis, had marginally nonsignificant time X competitor interactions but no treatment differences in survival. Finally, a second uncommon rodent, Abrocoma bennetti (not analyzed numerically) had significantly longer survival on predator exclusion grids with degus. Degus and P. darwini were significantly overrepresented (relative to availability) in diets of culpeo foxes (Pseudalopex culpaeus) and three nocturnal owls, respectively, whereas A. bennetti was significantly overrepresented in predator diets generally. Vertebrate predation has pervasive effects on some species that, however, may be related to their intrinsic demographic characteristics. Competition may be mediated by subtle behavioral interactions among assemblage members. Long-term studies are necessary to elucidate the role of biotic and abiotic factors in semiarid environments.

Effects of livestock on the feeding ecology of endemic culpeo foxes (Pseudalopex culpaeus smithersi) in central Argentina

“…These results contradict recent findings for coyotes (Sacks & Neale 2002) and selectivity results for culpeos in another study (Novaro et al 2000). Culpeo studies in central and northern Chile (e.g., Iriarte et al 1989, Ebensperger et al 1991, Jiménez et al 1996, Meserve et al 1996 did not obtain availability data for prey other than small mammals, so their selectivity results cannot be compared to ours. Data from Argentine Patagonia PIA ET AL.…”

“…Culpeos are opportunistic predators but can be locally selective for certain prey, consuming mainly small mammals and introduced lagomorphs (Lepus eurapaeus, Pallas 1778; Oryctolagus cuniculus, Linnaeus 1758) (Novaro 1997). Some studies have assessed culpeo prey selection (e.g., Iriarte et al 1989, Jaksic et al 1992, Johnson & Franklin 1994, Meserve et al 1996, Novaro et al 2000, but none have analyzed prey availability and selection in areas with different livestock abundance.…”

Long-term dynamics of rodent populations in arid Australia: the influence of rainfall

“…Such studies have been pursued successfully on rodents of the Americas (e.g. Brown et al 1986;Meserve et al 1996), and will be essential to produce a more mechanistic understanding of rodent population dynamics in arid Australia.…”

“…In North America, for example, the numbers of several species of small granivorous rodents are often depressed by the presence of larger and competitively superior rodents (Brown et al 1986;Heske et al 1994) or by granivorous ants (Brown and Davidson 1977). In semi-arid Chile, predation has been demonstrated to depress rodent numbers, especially species with predictable population cycles (Meserve et al 1993(Meserve et al , 1996. Indirect and facilitatory interactions may also occur among rodents and other granivores (Thompson et al 1991), but population-level effects have been little studied.…”

From coexistence to competitive exclusion: can overfishing change the outcome of competition in skates (Chondrichthyes, Rajidae)?

“…Most of the best evidence for competition in vertebrate communities comes from small-scale experiments (in the scale of m 2 or at most hectares) and from small-bodied organisms, such as small fishes (Schmitt & Holbrook, 1999), lizards (Petren & Case, 1996) and small mammals (Meserve et al, 1996). While controlled experiments provide the most unambiguous evidence for competition, their unfeasibility at large scales makes them impractical to study the importance of competition in large-scale communities (Connell, 1983).…”