Selection on plant height through the interplay of landscape and large herbivores

Abstract

Many herbaceous and graminoid plants from open communities are characterized by their relatively small size and by seeds that appear to lack any clear traits for dispersal. Such syndrome is likely the result of several selective pressures and their tradeoffs acting together. Drawing on the putative relationship of these plants with large mammals that graze on them, with respect to defoliation and the dispersal of seeds (endozoochory), we included plant stature as a trait in a simulation model to elaborate on these animals relative contribution in plant evolution. Different configurations of the landscape were used as a template, as these are known to affect the response of plants through additional costs levied in dispersal. As such, two herbivore parameters (the intensity of grazing and the efficacy of endozoochorous dispersal) were tested along with two parameters of the landscape (the proportion and connectivity of suitable habitat). Plants were allowed to evolve freely under these conditions, assuming that taller plants 1) produce more seeds and 2) have a more distant seed rain in wind dispersal, but 3) are also more likely to suffer failed reproduction because of herbivory. Our model confirmed the effects of landscape on the resulting dispersal capacity of plants, although these effects were readily overruled by the actions of grazers. We found the evolution of plant size to primarily result from the effects of defoliation, but also (though to a lesser degree) from endozoochory. This provides support for the adaptive value of unassisted dispersal syndromes in plants. Endozoochory also succeeded in maintaining increased population densities. However, these effects only hold when grazers sustain a considerable transfer of seeds towards suitable plant habitat

Integrating movement ecology with biodiversity research - exploring new avenues to address spatiotemporal biodiversity dynamics

“…Disappearance of these animals will seriously impact the spatial distribution of plant species and ultimately biodiversity patterns. The same probably holds for other systems as well, including savanna systems, forests and grasslands [ 40 , 41 , 59 , 74 , 75 ]. Depending on the type of movement (e.g.…”

“…Scattering seeds may reduce predation, but plants growing in close vicinity and/or in clumps may have advantages in pollination [ 40 ]. Foraging behavior can also affect the distribution and fate of seeds in grasslands directly through endozoochory as well as change dispersal capacity and evolutionary dynamics [ 41 ].…”