Spatial scale and opportunities for choice influence browsing and associational refuges of focal plants
Miller, AM and McArthur, C and Smethurst, PJ, Spatial scale and opportunities for choice influence browsing and associational refuges of focal plants, Journal of Animal Ecology, 78, (6) pp. 1134-1142. ISSN 0021-8790 (2009) [Refereed Article]
1. Foraging decisions by herbivores depend on variation in food types, the scale(s) at which this
variation occurs and the opportunity and capacity for herbivores to respond to such variation.
These decisions affect not only the herbivores themselves, but also the vulnerability of individual
plants to being eaten. Associational plant refuges, in which neighbouring plants alter focal plant
vulnerability, are an emergent property of foraging decisions.
2. Using the red-bellied pademelon (Thylogale billardierii) as a model generalist mammalian herbivore,
we investigated the spatial scale(s) at which animals made foraging decisions and the resultant
effect on focal plant vulnerability. In a replicated design, we varied vegetation at the
individual plant scale, generating intraspecific differences in Eucalyptus nitens seedlings by altering
their nutrient status (high, low). We varied vegetation at the patch scale, in which seedlings were
planted, using high- (grass) and low- (herbicided) quality patches. Animals were allowed to choose
where they fed and what they ate. Animal behaviour was recorded and intake of seedlings
3. We found that animals made foraging decisions first at the patch scale then at the scale of individual
plants; both patch and focal seedling characteristics influenced browsing. Pademelons spent
most of their time in high-quality patches, and seedlings were consequently more vulnerable there
than in low-quality patches. Pademelons also ate more foliage from high- than from low-nutrient
status seedlings. This behaviour concentrated resources, increasing foraging efficiency and making
focal plants more vulnerable to browsing.
4. The opportunity and capacity to choose at both plant and patch scales resulted in a pattern of
focal plant vulnerability consistent with the repellent-plant hypothesis. This contrasts with our previous
study, in which animals were only provided with choice at the plant level and plant vulnerability
followed the attractant-decoy hypothesis. These combined results demonstrate that the
influence of neighbouring vegetation on consumption of a focal plant depends on the spatial scale
of selection and on opportunities (and capacity) for herbivores to choose.