Abstract
Carnivorous plants allocate more resources to carnivorous structures under nutrient-limited conditions, and relative investment can also be influenced by animals (infauna) that live in association with these plants and feed on their prey. We investigated these effects within a population of the pitcher plant Cephalotus follicularis containing varying densities of larvae of the fly Badisis ambulans. For plants with a relatively high proportion of adult pitchers, increasing larval density was associated with lower relative leaf allocation to new pitcher buds. For plants with relatively few adult pitchers, however, there was greater relative leaf allocation to pitcher buds with increasing larval density. In a field experiment, there was no significant effect of experimental larval presence or absence on the change in carbon-to-nitrogen (C/N) ratio of plants. Although the direction of the correlation between B. ambulans larvae and relative investment in carnivorous and non-carnivorous structures depends on the relative number of mature structures, whether the larvae enhance or reduce nutrient stress under different conditions remains unclear. The change in C/N was, however, less variable for pitchers that contained larvae, suggesting a stabilizing effect. Eighteen of 52 experimental pitchers were damaged by an unknown species, causing the pitcher fluid to drain. These pitchers were significantly more likely to survive if they contained larvae. These results suggest that the relationship between infauna and host varies with the initial resource status and environmental context of the host plant.
Highlights
Carnivorous plants typically respond to changing nutrient conditions by changing relative investment in different structures
We examined the relationship between infauna density and (i) the relative number of new carnivorous structures and (ii) nutrient status of plant tissues in the Albany pitcher plant, Cephalotus follicularis, a vulnerable species which is phylogenetically distinct from other pitcher plants and found only in the margins of peat swamps in the Southwest Australian Floristic region [21,22,23,24,25,26]
We examined whether the density of B. ambulans within pitchers was associated with relative investment in carnivorous structures by the plant, and/or changes in plant nutrient status (carbon-to-nitrogen (C/N) ratio) that might be influenced by altered assimilation of nutrients from prey
Summary
Carnivorous plants typically respond to changing nutrient conditions by changing relative investment in different structures. The cost–benefit model of plant carnivory [1] assumes that carnivory should be favoured only when the productivity benefits from added nutrients outweigh the energetic costs of producing carnivorous structures, which are inefficient for other functions such as light-harvesting. Plants under more nutrient-limited conditions should allocate a greater proportion of their resources to carnivorous structures [2,3,4,5]. These responses, may not be determined only by environmental nutrient availability, and by relationships with symbiotic animal species. Any examination of the nature (mutualism or parasitism) of the plant–infauna relationship should not be limited to an examination of the effect of infauna on carnivorous investment, but should be coupled with an examination of the nutrient status of the host
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