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Seed dispersal by carnivores in temperate and tropical dry forests

Citation

Rubalcava-Castillo, Fabián Alejandro et al. (2021), Seed dispersal by carnivores in temperate and tropical dry forests, Dryad, Dataset, https://doi.org/10.5061/dryad.c866t1g5m

Abstract

The seed dispersal mechanisms and regeneration of various forest ecosystems can benefit from the actions of carnivores via endozoochory. This study aims to evaluate the role of carnivores in endozoochory and diploendozoochory, as well as their effect on seed viability, scarification, and germination in two forest ecosystems: temperate and tropical dry forest. We collected carnivore scat in the Protected Natural Area of Sierra Fría in Aguascalientes, Mexico, for two years to determine the abundance and richness of seeds dispersed by each carnivore species, through scat analysis. We assessed seed viability through optical densitometry using X-rays, analyzed seed scarification by measuring seed coat thickness using a scanning electron microscope, and evaluated seed germination in an experiment as the percentage of seeds germinated per carnivore disperser, plant species, and forest type. In the temperate forest, four plant species (but mainly Arctostaphylos pungens) were dispersed by four mammal species. The gray fox dispersed the highest average number of seeds per scat (66.8 seeds). Bobcat dispersed seeds through diploendozoochory, which was inferred from rabbit (Sylvilagus floridanus) hair detected in their scats. The tropical dry forest presented higher abundance of seeds and richness of dispersed plant species (four species) than in the temperate forest, and the coati dispersed the highest number of seeds (8639 seeds). Endozoochory and diploendozoochory did not affect viability in thick testas seeds in temperate forest and thin testas seeds in tropical dry forest. Endozoochory improved the selective germination of seeds. Nine plant species were dispersed by endozoochory, but only one species (Juniperus sp.) by diploendozoochory. These results suggest that carnivores can perform an important ecological function by dispersing a great abundance of seeds, scarifying these seeds causing the formation of holes and cracks in the testas without affecting viability and promoting the selective germination of seeds.

Methods

The database includes the location by UTM coordinates of each of the scats found during the study period. Each scat has a code that represents: R = Ringtaill, G = Gray fox, C = Coyote, BO = Bobcat, BA = Badger and CO = Coati. We conducted field visits in each site once a month throughout the years of 2018 and 2019. Within each site, we collected scats located by sight within transects of following walking routes through the study area to locate scats by sight. Each transect is delimited by a central line of 2 km in length, with two parallel lines located at a distance of 20 m on either side of the central line. We have established a total of 30 transects in each area on trails for the movement of fauna, on dirt roads and among vegetation, i.e., the scats were screened over a total area of 2 (temperate, tropical dry forest) x 30(replicate transects) x 2000 m (transect length) x 40m (transect width/buffer). We collected all the scats found within the transect for identification, except for those that were dry and old, with a gray coloration, to avoid bias in the data related to the collection of old scats and a preference of collection towards specific animals. Thus, each transect was sampled twice during the study period. Scats corresponding to each mammalian species were identified based on the Manual for Tracking the Wild Mammals of Mexico.