Associational effects of plant defences in relation to within- and between-patch food choice by a mammalian herbivore: neighbour contrast susceptibility and defence

Abstract

A basic idea of plant defences is that a plant should gain protection from its own defence. In addition, there is evidence that defence traits of the neighbouring plants can influence the degree of protection of an individual plant. These associational effects depend in part on the spatial scale of herbivore selectivity. A strong between-patch selectivity together with a weak within-patch selectivity leads to a situation where a palatable plant could avoid being grazed by growing in a patch with unpalatable plants, which is referred to as associational defence. Quite different associational effects will come about if the herbivore instead is unselective between patches and selective within a patch. We studied these effects in a manipulative experiment where we followed the food choice of fallow deer when they encountered two patches of overall different quality. One of the two patches consisted of pellets with low-tannin concentration in seven out of eight buckets and with high concentration in the remaining bucket. The other patch instead had seven high- and one low-tannin bucket. We performed the experiment both with individuals one at a time and with a group of 16-17 deer. We found that the deer were unselective between patches, but selective within a patch, and that the single low-tannin bucket among seven high-tannin buckets was used more than a low-tannin bucket among other low-tannin buckets. This corresponds to a situation where a palatable plant that grows among unpalatable plants is attacked more than if it was growing among its own kind, and for this effect we suggest the term neighbour contrast susceptibility, which is the opposite of associational defence. We also found that the high-tannin bucket in the less defended patch was less used than the high-tannin buckets in the other patch, which corresponds to neighbour contrast defence. The neighbour contrast susceptibility was present both for individual and group foraging, but the strength of the effect was somewhat weaker for groups due to weaker within-patch selectivity.

Woody Plant-Herbivore Interactions in Semi-Arid Savanna Ecosystems

“…When palatable plants gain protection from their unpalatable neighbours the phenomenon is referred to as associational defence (McNaughton, 1978;Hjalten et al, 1993). However, palatable plants are usually susceptible to attack when they occur in a patch with unpalatable neighbours, a situation referred to as neighbour contrast susceptibility (Bergvall et al, 2006). …”

Palatability mapping: a koala's eye view of spatial variation in habitat quality

“…Plants experience associational defense or associational resistance when they benefit from reduced herbivory because of their association with neighboring plants, and associational susceptibility if the association is detrimental (Atsatt andO'Dowd 1976, Barbosa et al 2009). A plant can experience associational resistance from unpalatable neighboring plants when herbivores make foraging decisions at the scale of a patch of plants, or by association with palatable neighbors if they act as attractant-decoys when herbivores forage at an individual-plant scale (Bergvall et al 2006). Whether such associational effects occur, and whether spatial patches of trees of similar palatability are of any significance to foraging herbivores thus depends upon the scale of the herbivore's foraging movements (Milchunas and Noy-Meir 2002).…”

Induction of low-nutritious food intake by subsequent nutrient supplementation in sheep (Ovis aries)

“…One general implication sustained by the present results and the literature on incentive relativity is that the animal responds and learns about foods beyond their intrinsic (e.g. nutritional) properties: whether food incentives are presented in isolation, combination or sequence matters (see Flaherty, 1996;Bergvall et al 2006 and2007;Catanese et al, 2010 and2011, for examples in ruminants). This may be a consequence of learning and comparative processes, as well as nutritional and digestive interactions among foods, and should be taken into account when intending to affect animals' diet selection.…”

“…For instance, the specific array of plants encountered and the sequence of encounters could turn out to be crucial in -E-mail: efreidin@criba.edu.ar, efreidin@yahoo.com determining nutritional consequences, as well as the level of consumption of each species in ruminants (e.g. see Meuret et al, 1994;Meuret, 1996;Villalba and Provenza, 2005;Bergvall et al, 2006 and2007). These effects that transcend what would be expected based on the intrinsic properties of plants may occur because of digestive synergies (or antagonisms) among foodstuffs, associative learning and comparison processes or the interaction between these mechanisms.…”