Plant-animal interactions: The search for general interaction rules brings energetic traits into focus

Alexander Neu, Huw Cooksley, Karen J. Esler, Anton Pauw, Francois Roets, Frank M. Schurr, Matthias Schleuning

This is a plain language summary of a Functional Ecology research article which can be found here.

Plants and animals interact in different ways with each other. Interactions can be positive for both partners (e.g., mutualistic interactions between plants and their pollinators), or they can be positive for one and negative for the other partner (e.g., antagonistic interactions between plants and their herbivores). So far, it is little known whether similar types of functional traits shape mutualistic and antagonistic plant-animal interactions.

We addressed this question by studying Protea plants and their mutualistic pollinators, as well as their antagonistic seed herbivores in South African heathlands. Protea plants generate copious amounts of nectar, show a morphological diversity and are pollinated by insects, birds and mice. Furthermore, most Proteas retain their seeds until after a bushfire. Hence, the seeds remain in cones on the mother plant for years and are therefore an important food source for many herbivorous animals in these nutrient-poor heathlands.

Cape Sugarbird (Promerops cafer) pollinating Protea neriifolia (credit: Alexander Neu)

To address our question, we recorded interactions between Protea plants and their animal mutualists and antagonists at 21 study sites. In addition, we measured traits related to energetic plant rewards (i.e., nectar and seeds) and energetic animal demands (i.e., metabolic rates). We also measured morphological traits describing the size and shape of Protea inflorescences and seed-retaining cones, as well as the size and shape of animal mutualists and antagonists.

We found consistent effects of energetic traits on interactions between plants and their animal mutualists and antagonists. In general, large animals with high metabolic demands dominated energy-rich resources, whereas smaller animals were displaced towards less rewarding resources. In contrast, effects of morphological traits on plant-animal interactions were more variable. Inflorescence shape and morphological defense against seed predation were important, but the shape of relationships was variable across animal taxa and interaction types.

Our findings suggest that energetic traits may be useful to predict interactions between plants and their animal mutualists and antagonists and, prospectively, predict plant-animal interactions in current and future communities.


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