Abstract
The process of seed dispersal of many animal-dispersed plants is frequently mediated by a small set of biotic agents. However, the contribution that each of these dispersers makes to the overall recruitment may differ largely, with important ecological and management implications for the population viability and dynamics of the species implied in these interactions. In this paper, we compared the relative contribution of two local guilds of scatter-hoarding animals with contrasting metabolic requirements and foraging behaviours (rodents and dung beetles) to the overall recruitment of two Quercus species co-occurring in the forests of southern Spain. For this purpose, we considered not only the quantity of dispersed seeds but also the quality of the seed dispersal process. The suitability for recruitment of the microhabitats where the seeds were deposited was evaluated in a multi-stage demographic approach. The highest rates of seed handling and predation occurred in those microhabitats located under shrubs, mostly due to the foraging activity of rodents. However, the probability of a seed being successfully cached was higher in microhabitats located beneath a tree canopy as a result of the feeding behaviour of beetles. Rodents and beetles showed remarkable differences in their effectiveness as local acorn dispersers. Quantitatively, rodents were much more important than beetles because they dispersed the vast majority of acorns. However, they were qualitatively less effective because they consumed a high proportion of them (over 95%), and seeds were mostly dispersed under shrubs, a less suitable microhabitat for short-term recruitment of the two oak species. Our findings demonstrate that certain species of dung beetles (such as Thorectes lusitanicus), despite being quantitatively less important than rodents, can act as effective local seed dispersers of Mediterranean oak species. Changes in the abundance of beetle populations could thus have profound implications for oak recruitment and community dynamics.
Highlights
Plant-animal interactions are key components in the regeneration process of many plant species with strong implications for population viability and community dynamics [1,2]
We aimed to answer the following questions: (i) What is the comparative effectiveness of rodents and dung beetles as local acorn dispersers of oak species in a Mediterranean forest of southern Spain?; (ii) Which one of the two seed dispersal effectiveness (SDE) components better contributes to overall short-term recruitment of these oak species?; (iii) How do these plant-animal interactions change with microhabitat conditions?; and (iv) What are the ecological and management implications of these findings for forest stand dynamics and species conservation?
The percentage of seeds handled by rodents was significantly higher under shrubs compared with the other two types of microhabitats, these differences disappeared as seed handling approached 100% (Figs. 1A and 1B)
Summary
Plant-animal interactions are key components in the regeneration process of many plant species with strong implications for population viability and community dynamics [1,2]. The qualitative component of SDE depends on other factors such as the probability that a dispersed seed remains viable after the activity of the dispersal agent or the recruitment suitability of the microhabitat where the seed is deposited [6]. Most studies linking seed dispersal and plant demography have focused on early demographic processes, such as seedling emergence and first-year survival, often ignoring the delayed consequences of seed deposition at later stages of recruitment [8]. Since the suitability for recruitment of different microhabitats may change over the life cycle of the plant [9,10], studies based only on early life-history stages can lead to incomplete and misleading conclusions
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