Herbivore feeding preferences in captive and wild populations

Abstract

Investigations into the mechanisms underpinning plant selection by herbivores have often yielded conflicting results. Such inconsistency might stem from whether selection experiments are conducted with captive or wild populations, and upon the different measures of plant selection used to determine herbivore preference.Here we compared the feeding preferences of captive and wild kangaroos (Macropus fuliginosus) using a standard set of plant species (14 Hakea spp., Proteaceae) and several measures of herbivore selection to examine how environment influenced relative consumption. Three indices of herbivore consumption were measured: number of plants (NP), total shoot volume per plant (TV) and percentage available shoot volume (PV) consumed. NP and TV were closely correlated in the wild and captive populations and consistently correlated with six morphological and chemical plant attributes examined, the most notable being a strong negative correlation with shoot phenolic content. This uniformity suggests that plant selection by captive kangaroos is broadly consistent with that observed in field trials, and consequently that for macropods, at least, captive trials offer a valid way to determine the relative acceptability of different plant species. However, the fact that our third measure of herbivore selection PV was weakly correlated in captive and wild populations and showed no relationship with shoot phenolic content highlights the importance of which measure of plant selection is applied. We suggest that, while NP and TV are potentially confounded by plant size and availability, they offer the clearest insight into plant selection from the point of view of the herbivore, while PV is more suitable for plant-centred studies.

LMA, density and thickness: recognizing different leaf shapes and correcting for their nonlaminarity

“…Or the problem is ignored by treating leaves as flat even when they are not. Even when the problem is recognized, attempts to correct planar leaf area for variations in the third dimension of needle leaves have varied from reducing it slightly (Rafferty et al ., – to correct for actual V in using LMA as an index of herbivore resistance) to increasing it greatly (Shi et al ., – to highlight total surface area from a gas exchange viewpoint). Since the type of correction is usually a constant when used within plants or species, its actual value is of little biological significance; but when LMA is compared between species (and studies) the existence or magnitude of a correction might have a major effect on meaning of the data.…”

Low Rate of Between-Population Seed Dispersal Restricts Genetic Connectivity and Metapopulation Dynamics in a Clonal Shrub

“…Large seeds and seedlings are often more visible and attractive to granivores and herbivores [53], [54]. As such, seeds of B. candolleana may be favoured by granivores.…”

Contribution of transition and stabilization processes to speciation is a function of the ancestral trait state and selective environment in Hakea

“…Reversals were negligible indicating strong directional selection. Why more events did not yield spiny leaves is partly attributable to morphological constraints, the fact that all Hakea leaves are highly unpalatable and not grass-like (Rafferty et al , 2010), and ability of vertebrates to learn to overcome physical deterrents (Hanley et al , 2007).…”

“…Nutrient-poor, fire-prone, Mediterranean-type regions with a prolonged hot, dry season and exposed to intensive pressure from pollinators, herbivores and granivores are characterised by high species richness and endemism (Cowling et al , 1996) and should provide suitable scenarios to examine these issues. Hakea is a shrub genus of over 150 species, spread throughout Australia but best represented in mediterranean southwestern Australia, and renowned for its great variation in leaf and fruit morphology, pollinators, climate and fire tolerances and susceptibility to herbivores and granivores (Groom and Lamont, 1996a, 1997, 2015; Lamont et al , 2015, 2016; Hanley et al , 2009, Rafferty et al , 2010).…”