Abstract
Herbivores can play an important role as seed dispersal vectors, ungulates constituting potential seed dispersal agents of Mediterranean grasses and shrubs. We evaluated the role of domestic goats as seed dispersers of five representative Mediterranean forage shrub species (Cistus albidus L., Phillyrea angustifolia L., Calicotome villosa (Poir.) Link., Rhamnus lycioides L. and Atriplex halimus L.). Following seed ingestion by goats, total faeces were collected at 24-h intervals for five days. The total number of seeds recovered varied among species, with R. lycioides showing the minimum recovery percentage (1.3%) and C. albidus (35.8%), the maximum. Seed recovery was significantly related to seed hardness and length. In most species, the maximum amount of seeds recovered occurred 48-72 h after ingestion. The passage through the goat gut significantly depressed seed germination in C. albidus, C. villosa and A. halimus; inhibited it in R. lycioides and increased it in P. angustifolia. Seedling emergence was significantly lower in intact dung pellets than in broken-down ones, and both significantly lower than in uneaten seeds (control). The results of this study show that goats can potentially favor or inhibit seed dispersal of browsed Mediterranean shrub species. Therefore, goat grazing could be a potential management tool for expanding target shrub species populations or preventing shrub encroachment in undesired areas.
Highlights
Endozoochory has been extensively studied in the past, and has recently gained new momentum
At the beginning of the experiment, each goat was offered a high number of seeds from each species (21,388 seeds: 5,000 seeds of the species C. albidus, P. angustifolia, R. lycioides and A. halimus, plus 1,388 seeds of C. villosa) in order to ensure that some passed the goats guts
The average number of seeds retrieved from daily subsamples was extrapolated to the total daily dung amount per animal, providing an estimate of the daily percentage of seed recovery (PR) through the following expression: PR = [(Mf · Sr) / 4S] *100, where Mf is the total daily mass of faeces, Sr is the average number of seeds retrieved per subsample (4 g of pellet), and S is the number of seeds ingested per goat (Mancilla-Leytón et al, 2012)
Summary
Endozoochory has been extensively studied in the past, and has recently gained new momentum. The role of herbivorous mammals as endozoochorous seed dispersers has been recently highlighted (Willson, 1993; Pakeman et al, 2002; Myers et al, 2004), and several studies have proved the presence of seeds in the dung of wild and domestic herbivores (Sánchez & Peco, 2002; Manzano et al, 2005; Ramos et al, 2006; Kuiters & Huiskes, 2010; De la Vega & Godínez-Álvarez, 2010; Mancilla-Leytón et al, 2011, 2012). Since herbivorous mammals have a long seed residence time in guts (24 to 72 h) (Olson & Wallander, 2002; Mancilla-Leytón et al, 2011) and make long-distance routes (Cory, 1972; Klein, 1981), they can promote the rapid dispersal of plant populations. Due to the particular feeding habits and ranging behavior of browsers (Morand-Fehr et al, 1983; Devendra, 1990; Milne, 1991), herbivores such as domestic goats can be seed dispersers.
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