Adult free zones in small mammal populations: response of Australian native rodents to reduced cover

Abstract

Cover provides shelter, food, nesting opportunities and protection from predators. The behavioural response of small mammals to reduced cover has been well documented. However, very little is known about the effect of cover on community and population dynamics. Australian small mammals generally inhabit extremely dynamic ecosystems, where cover and food supplies are greatly affected by fire. Species are described as early or late seral specialists, generally returning to a disturbed area once their habitat requirements are met. Habitat requirements have loosely been interpreted as cover and food supply, however, these factors are not mutually exclusive and few studies have attempted to determine the driving factors behind small mammal succession. In this study, we manipulated specific aspects of cover in the eucalypt forests of Fraser Island and show that the behaviour and population dynamics of small mammals were greatly affected. A reduction of cover from grass-trees ( Xanthorrhoea johnsonii ) did not affect small mammal species composition, however, the abundance and size structure distribution of the dominant species ( Rattus fuscipes ) decreased. Patch use by rodents also decreased after cover was reduced. Rattus fuscipes must trade-off remaining in an environment with increased risk of predation, or disperse to an area with greater cover but increased competition. Juveniles dominated ( > 60%) populations of R. fuscipes after cover was reduced, however, size distributions of control sites were relatively more even ( < 25% juvenile). While adult R. fuscipes are either killed by predators or disperse to other areas, juveniles that remained or immigrated to an area of reduced cover gained a selective advantage over those in control sites, because reduced competition with adults increased body condition of juvenile R. fuscipes .

Differing responses to landscape change: implications for small mammal assemblages in forest fragments

“…The characteristics of habitat fragments may be significantly altered by processes including edge effects and anthropogenic disturbances (Saunders et al 1991;Hobbs 2001;Kupfer et al 2006;Fischer and Lindenmayer 2007). Changes to vegetation characteristics can dramatically influence the suitability of sites for fauna (Spencer et al 2005;Luther et al 2008). Thus, the distribution of species in modified landscapes is likely to be influenced by both local habitat characteristics and biogeographic parameters (Thomas et al 2001;Fleishman et al 2002;Armstrong 2005).…”

“…Fragmentation causes two key changes to the spatial attributes of habitat that, in turn, have detrimental consequences for fauna: (1) a reduction in the size of habitat fragments, and (2) an increase in the distance between fragments (Saunders et al 1991;Fischer and Lindenmayer 2007). As fragments become smaller, animal populations decline in size, resulting in an increased risk of extinction (Soulé 1987). Isolation restricts interfragment movements, thereby reducing the likelihood of population supplementation and colonisation of unoccupied habitat.…”

Use of Xanthorrhoea semiplana (grass-trees) for refuge by Rattus fuscipes (southern bush rat)

“…The 50% reduction in availability of grass-trees at Site 2 compared with Site 1 did not seem to make any difference in selection of grass-trees by bush rats for cover. Spencer et al (2005) also found that bush rats relied on grass-trees for shelter. These authors reduced the total cover available from X. johnsonii by over 45% by tying overhanging foliage of grass-tree canopies in tight clumps close to the stem of the plant.…”

“…Spencer et al (2005) noted that the abundance of Rattus fuscipes (southern bush rat) decreased with a reduction in cover of X. johnsonii on Fraser Island. The study by Spencer et al (2005) and brief mentions of animal and grass-tree associations in other papers validated the need for a detailed study of the role of grass-trees as refuges for wildlife in the Mount Lofty Ranges.…”

“…It has a trunk shorter than 1 m, and sometimes none at all, and a circular canopy of grass-like, long, and narrow leaves that bend downwards and touch the ground as the plant grows. In a mature tree, the leaves form a dense canopy (Dashorst and Jessop 1998;Lamont et al 2000;Neagle 2004) and can provide a large area of shelter for ground-dwelling mammals (Spencer et al 2005).…”