Selective feeding by kangaroos (Macropus fuliginosus) on seedlings of Hakea species: Effects of chemical and physical defences

Abstract

In this experiment we investigate how chemical and physical attributes affect the grazing of 14 species of Hakea (Proteaceae) seedlings by western grey kangaroos (Macropus fuliginosus). Needle-leaved Hakeas were preferred over broad-leaved congeners, although differences between species within these groups were sometimes large. Needle-leaved species had smaller, thicker and spinier leaves with lower phenolic contents, but similar nitrogen contents (except for high levels in H. platysperma). The three tallest needle-leaved species, with longest, most upright and thickest leaves (H. adnata, H. obliqua and H. platysperma) were most preferred. Principal components analysis on attributes of the 14 species showed that the relative volume of shoot material consumed was significantly related (inversely) to phenolic content. Chemical defences therefore appear to have a significant deterrent role at this stage in the plant?s life history. Physical defences however were ineffective deterrents against kangaroo herbivory raising the possibility that other ecophysiological factors contribute to the possession of structures such as spines and sclerophylly in young seedlings.

Defence against vertebrate herbivores trades off into architectural and low nutrient strategies amongst savanna Fabaceae species

“…As such, it might be argued that the patterns we observed are true only for Fabaceae. Evidence from studies of co‐occurring spinescent and non‐spinescent Hakea species (Proteaceae) growing in southwestern Australia do support our findings: Rafferty et al () found a negative relationship between leaf N and spine density, and Hanley and Lamont () found a negative relationship between leaf area and spinescence, among species of the genus. More formal comparison under common conditions is required to properly confirm the consistency of the tradeoff, and it is our intention to extend our research to cover species from a wider range of woody families.…”

Unintended Consequences of Invasive Predator Control in an Australian Forest: Overabundant Wallabies and Vegetation Change

“…However, di Stefano and Newell [33] showed that bracken was not a preferred food of swamp wallabies. Subtle differences in phenolics within plant families [74] and within individual genera [75] can have profound impacts on the browsing pressure to which individual plant species are exposed. The substantial impact of browsing on C. monilifera is in accord with the finding of Scurr et al [46] that browsing by macropods and domestic livestock limited the distribution of the conspecific boneseed Chrysanthemoides monilifera ssp.…”

Plant ontogeny and chemical defence: older seedlings are better defended

“…Similar effects have been demonstrated in many other ecosystems, including tropical forests (Asquith and Mejia‐Chang 2005), Mediterranean‐climate scrublands (Izhaki and Ne'eman 1997), and European temperate grasslands (Hanley et al 1995a). Seedling selection by herbivores is based on the deployment of various chemical and physical plant defences (Hanley and Lamont 2001, Rafferty et al 2005), seedling age and size (Hanley et al 1995b, Vasconcelos and Cherrett 1997), spatial associations between seedlings (Hanley et al 1995b), and the identity of the herbivore involved (Hulme 1994). However, while the basis of seedling selection is relatively well established, we understand remarkably little about interactions between the factors that underpin patterns of seedling selection.…”