Are tortoises important seed dispersers in Amazonian forests?

Abstract

According to most studies on seed dispersal in tropical forests, mammals and birds are considered the main dispersal agents and the role played by other animal groups remains poorly explored. We investigate qualitative and quantitative components of the role played by the tortoise Chelonoidis denticulata in seed dispersal in southeastern Amazon, and the influence of seasonal variation in tortoise movement patterns on resulting seed shadows. Seed shadows produced by this tortoise were estimated by combining information on seed passage times through their digestive tract, which varied from 3 to 17 days, with a robust dataset on movements obtained from 18 adult C. denticulata monitored with radio transmitters and spoon-and-line tracking devices. A total of 4,206 seeds were found in 94 collected feces, belonging to 50 seed morphotypes of, at least, 25 plant genera. Very low rates of damage to the external structure of the ingested seeds were observed. Additionally, results of germination trials suggested that passage of seeds through C. denticulata's digestive tract does not seem to negatively affect seed germination. The estimated seed shadows are likely to contribute significantly to the dispersal of seeds away from parent plants. During the dry season seeds were dispersed, on average, 174.1 m away from the location of fruit ingestion; during the rainy season, this mean dispersal distance increased to 276.7 m. Our results suggest that C. denticulata plays an important role in seed dispersal in Amazonian forests and highlight the influence of seasonal changes in movements on the resulting seed shadows.

Can tortoises facilitate the germination of plants with dry fruits? A simulation of the effects of Chelonoidis carbonarius (Testudines: Testudinidae) on the germination of Leucaena leucocephala (Fabaceae)

“…The neutral effect of acidic conditions on seed germination could suggest that C. carbonarius could disperse seeds of L. leucocephala, because the animal could transport seeds of this plant for long distances after eat them, and they would still be able to germinate. This mechanism was already suggested by some authors for other species of turtles and tortoises (Jerozolimski et al 2009;Kimmons & Moll 2010;Padget et al 2010). Seeds ingested by chelonians usually have low damage percentage (Kimmons & Moll 2010;Padget et al 2010), reinforcing the neutral effect on germination rates highlighted before.…”

“…We should emphasize, however, that germinative capacity was maintained even after exposing the seeds to HCl. This maintenance of germination is common in seeds eaten by turtles and tortoises (Jerozolimski et al 2009;Kimmons & Moll 2010). The neutral effect of acidic conditions on seed germination could suggest that C. carbonarius could disperse seeds of L. leucocephala, because the animal could transport seeds of this plant for long distances after eat them, and they would still be able to germinate.…”

“…Turtles and tortoises are examples of animals that have fruits in their diets, and some studies found that these animals may influence the germination and dispersal of plants that they eat (e.g., Liu et al 2004;Strong & Fragoso 2006;Jerozolimski et al 2009;Padgett et al 2010;Blake et al 2012). The ingestion of seeds by these animals may increase or decrease the number of germinated seeds and the germination speed, which vary according to the plant species (Liu et al 2004).…”

Relações espaciais entre Ananas ananassoides (Bromeliaceae) e Tachigali vulgaris (Fabaceae) influenciando a estrutura florestal na transição Amazônia/Cerrado no Brasil

“…Ananas ananassoides (Baker) LB Sm., also known as wild pineapple, is a terrestrial bromeliad, perennial, and pollinated by animals (e.g., birds and tortoises), with an annual or intermediate flowering period (Jerozolimski et al 2009;Silveira et al 2010;Stahl et al 2012). This species is considered a pioneer once it presents small and photoblastic seeds and higher germination rates in areas with high luminosity (Silveira et al 2010).…”

Plant ecology meets animal cognition: impacts of animal memory on seed dispersal

“…To date, much research on frugivores has focused mainly on observations of their behaviour, assessing their quality as dispersers on the basis of the amount of fruit eaten, the number of seeds processed, the number of viable seeds contained in faeces and the estimation of long seed dispersal distance based on data on animal daily movement and gut retention time (e.g. Calviño-Cancela and Martín-Herrero 2009;González-Castro et al 2015;Jerozolimski et al 2009;Link and Di Fiore 2006;Schupp 1993;Strong and Fragoso 2006). Although highly informative, this approach lacks predictive power in the face of ecosystem disruption because the cognitive determinants of the behaviour of seed dispersal vectors are largely unexplored.…”