Predicting Spatial Patterns of Plant Recruitment Using Animal-Displacement Kernels

Abstract

For plants dispersed by frugivores, spatial patterns of recruitment are primarily influenced by the spatial arrangement and characteristics of parent plants, the digestive characteristics, feeding behaviour and movement patterns of animal dispersers, and the structure of the habitat matrix. We used an individual-based, spatially-explicit framework to characterize seed dispersal and seedling fate in an endangered, insular plant-disperser system: the endemic shrub Daphne rodriguezii and its exclusive disperser, the endemic lizard Podarcis lilfordi. Plant recruitment kernels were chiefly determined by the disperser's patterns of space utilization (i.e. the lizard's displacement kernels), the position of the various plant individuals in relation to them, and habitat structure (vegetation cover vs. bare soil). In contrast to our expectations, seed gut-passage rate and its effects on germination, and lizard speed-of-movement, habitat choice and activity rhythm were of minor importance. Predicted plant recruitment kernels were strongly anisotropic and fine-grained, preventing their description using one-dimensional, frequency-distance curves. We found a general trade-off between recruitment probability and dispersal distance; however, optimal recruitment sites were not necessarily associated to sites of maximal adult-plant density. Conservation efforts aimed at enhancing the regeneration of endangered plant-disperser systems may gain in efficacy by manipulating the spatial distribution of dispersers (e.g. through the creation of refuges and feeding sites) to create areas favourable to plant recruitment.

Seed dispersal effectiveness in a plant–lizard interaction and its consequences for plant regeneration after disperser loss

“…In general, small seeds have usually longer retention times inside the digestive tract of dispersers than large seeds, which favours seed coat scarification (Traveset et al 2007 and references therein). In the present system, however, this does not seem to be the case, as retention time is independent of seed size (Santamaría et al 2007). In this latter work, the authors also found that larger seeds had higher chances of germination, but the effect of a larger size was reduced as retention time increased.…”

“…Under controlled conditions, seeds from lizards' scats have a similar viability to those collected and depulped directly from plants . Seeds within the pulp do not emerge (at least during a period of 2 years; Santamaría et al 2007), which further points out to the importance of lizards in the de-inhibition effect (Traveset et al 2007). Postdispersal seed predation (mostly by rodents) is consistently high across years and localities .…”

“…Since lizards can remain below shrubs for long periods (Santamaría et al 2007) and most D. rodriguezii adults grow under shrubs, we wanted to test for differences in seedling emergence and survival among nurse shrubs, information not previously obtained by Traveset and Riera (2005). On 2 December 2004, we sowed both lizardingested and non-ingested seeds in Colom Islet (Table 1), each including the three most representative microhabitats (physiognomically distinguishable patches of vegetation) where D. rodriguezii grows: under (1) conspecifics (Daphne hereafter), (2) P. latifolia (Phillyrea) and (3) P. lentiscus (Pistacia).…”

“…Certainly, more information is needed to support which one of the last hypotheses is responsible for the higher seedling emergence of the undisrupted population. Furthermore, lizards also remove the pulp around the seed (which is needed for germination to occur; Santamaría et al 2007) but most non-dispersed seeds are depulped by either ants or beetles ; pers. obs.).…”

Behavior Rather Than Diet Mediates Seasonal Differences in Seed Dispersal by Asian Elephants

“…Instead, our results suggest that the importance of disperser behavior may supersede the effects of disperser physiology and/or body size (similar to Spiegel andNathan 2007 andSantamarı´a et al 2007). The generality of this result is however questionable; instead, it should be taken to demonstrate that these factors play off against one another.…”