Spatial scales of foraging in fallow deer: Implications for associational effects in plant defences

Large herbivores select food at several spatial scales: plant communities are chosen at a landscape scale, plant patches are chosen within a plant community, and individual plants within a patch. Foraging decision at the patch level can result in associational effects in plant communities and populations. Several studies have shown that herbivore attack and consumption rates may not only depend on a plant's own defence traits, but also on the defence traits of its neighbours. In the present experiment we investigated whether the spatial scale of the food distribution affects food selection by fallow deer and whether the foraging behaviour gives rise to associational effects in plant defences. In a population of captured wild fallow deer we simulated a natural situation where two separate plant patches are exposed to intense herbivory pressure. We presented different spatial arrangements of low- and high-tannin food to the deer, varying the frequency of the feeder types within and between patches. We found that the deer consumed palatable food among the unpalatable food on average as much as they consumed palatable food among other palatable feeders. However, when unpalatable food occurred among the palatable food it was more consumed than among other unpalatable feeders. Hence, we did not find support for associational defence, but our results supported associational susceptibility. At the between patch level a patch of mainly high-tannin feeders was consumed less when presented near to a patch of mainly low-tannin feeders, suggesting that for well-defended plants having palatable neighbours in a nearby patch might accentuate the effectiveness of their defence.