Effect of seed passage through birds and lizards on emergence rate of mediterranean species: differences between natural and controlled conditions

Abstract

Summary1. The ingestion of fruits by vertebrate frugivores produces great variation on seed germination responses which depend on (1) the frugivorous species; (2) several factors intrinsic to the plant species; and (3) the conditions under which germination tests are conducted. Most studies on this topic have used only one or a few disperser species, and have been performed under controlled conditions. 2. The main goals of this study were to determine (1) the effect that birds ( Turdus merula ) and lizards ( Podarcis pityusensis ) have on seed emergence patterns of a group of common mediterranean plants; and (2) whether such patterns differ between field and common garden conditions. Over 2 years we compared seed emergence times with those of controls (pulp-removed seeds). 3. Emergence patterns were inconsistent for most plant species when comparing field vs. common-garden conditions. In some cases results were even contradictory: for instance lizards accelerated the emergence time of Rubus seeds in the field, but delayed it in the experimental garden; likewise Rubia seeds ingested by Blackbirds emerged more slowly than controls in the field, but faster than those in the garden. The two frugivorous species had also inconsistent effects on the same plant species. 4. Significant changes in seed weight after passage through the animals' digestive tracts were observed in most species. However, seed weight did not explain differences in seed emergence patterns between ingested and non-ingested seeds. 5. This study demonstrates the great heterogeneity in seed-emergence responses of the different plant species to ingestion by different types of frugivore, and to the different experimental conditions. Thus, caution is needed when making generalizations from studies that aim to evaluate the influence of frugivores on seed dispersal quality.

The importance of lizards as frugivores and seed dispersers.

“…and control (Valido, 1999;Nogales et al, 2005) all showed a similar percentage germination. An analogous result was also found by Rodríguez-Pérez et al (2005) for several Mediterranean plant species being dispersed by lizards and birds. Reanalysing their data, we found that seeds obtained from blackbird (Turdus merula) and Podarcis pityusensis (Lacertidae) droppings and controls resulted in a similar germination success for Rhamnus alaternus (Rhamnaceae), Rubia peregrina (Rubiaceae), Rubus ulmifolius (Rosaceae), Solanum luteum and Solanum nigrum (Solanaceae).…”

“…Klein, 1977;Janzen, 1982;Iverson, 1985;Traveset, 1990;Hartley et al, 2000) and the omnivorous ones (e.g. Whitaker, 1987;Fialho, 1990;Valido and Nogales, 1994;Willson et al, 1996;Lord and Marshall, 2001;Olesen and Valido, 2003;Rodríguez-Pérez et al, 2005).…”

Differential seed dispersal systems of endemic junipers in two oceanic Macaronesian archipelagos: the influence of biogeographic and biological characteristics

“…Since the highest percentage of germination (14.5%) was recorded in the first year (compared to 2.8% in the second year and 0% in the third), we decided to carry out the remaining experiments for only 1 year. As reported by Rodríguez-Pérez et al (2005), seed emergence patterns in germination experiments can be contradictory in some cases when comparing field versus greenhouse-garden conditions. For this reason, to examine the quality of dispersal, two in situ germination experiments were also performed at both sites during the rainy period (November 2008-March 2009 in Riscos de La Fortaleza; October 2008-June 2009 in Malha Grande).…”

Seed dispersal of Solanum thomasiifolium Sendtner (Solanaceae) in the Linhares Forest, Espírito Santo state, Brazil

“…Rodriguez-Perez et al (2005) showed great heterogeneity in seed-emergence responses of different plant species to ingestion by different types of frugivores, and to different experimental conditions. In our experiments seed germination rates were accelerated in relation to control (seeds from the fruit) when passing through the gut of lizard and delayed when passing through the gut of eating-crab-fox.…”