Dispersal of Dioon edule cycad seeds by rodents in a tropical oak forest in Mexico

Abstract

Predation of seeds of the cycad Dioon edule Lindl. by Peromyscus mexicanus (Saussure, 1860) has been previously documented, demonstrating that the seeds’ toxins are not harmful when combined with a varied diet. However, there is scarce evidence of P. mexicanus as a seed disperser. In a tropical oak forest in San Luis Potosí, Mexico, we experimented with seeds of D. edule and Quercus polymorpha Schltdl. & Cham., evaluating predators’ preference and recording it with photo-trapping. Burrows were sampled in concentric circles around a D. edule mother plant, and the types of burrows and condition of the seeds inside were identified with a borescope without destroying the burrows. The structure and composition of the forest were evaluated. The primary dispersion of D. edule seeds is by barochory. The rodents predate on seeds and prefer Q. polymorpha over D. edule (survival: 48.9% and 78.5%, respectively). There are more escape and multiple burrows at 3–6 m with mature oaks. Rodents forget or abandon D. edule seeds in the burrows, and such seeds germinate at 3–6 m. Peromyscus leucopus (Rafinesque, 1818) is a short-distance secondary disperser and predator of Dioon edule seeds.

Seed predation and potential seed dispersers of the narrow endemic Ceratozamia norstogii (Zamiaceae)

“…The low diversity of visitors reported here is consistent with other studies focused on cycads, where seed removal is carried out by a low diversity of small mammals, almost specifically ( Burbidge and Whelan 1982 , Snow and Walter 2007 , Hall and Walter 2013 , Yáñez-Espinosa et al 2021 , Monteza‐Moreno et al 2022 ). In addition, most of the species that interact with the cone represent sporadic visits ( Burbidge and Whelan 1982 , Snow and Walter 2007 ).…”

“…Three small mammals, the mouse, southern spotted skunk and the kinkajou, are reported here as potential seed dispersers of Ceratozamia norstogii . Mice as dispersers have also been observed in other species of cycads ( González-Christen 1990 , Snow and Walter 2007 , Yáñez-Espinosa et al 2021 ), but the spotted skunk and the kinkajou biting and carrying cycad seeds are recorded for the first time. Our results showed that the mouse of the genus Pteromiscus was a frequent visitor to the female cone of Ceratozamia norstogii and was observed biting and carrying seeds sarcotesta for several nights and for a long time, even when the cone was disintegrated and the seeds scattered on the ground (Figs 4 , 5 , 6 ,Suppl.…”

“…The spatial arrangement and density of cycad populations, with dense spatial aggregations of seeds and seedlings, could suggest dispersal by gravity. However, our results suggest an effect of short-distance seed dispersal mediated by small mammals (Burbidge and Whelan 1982,Snow and Walter 2007,Hall and Walter 2013,Yáñez-Espinosa et al 2021. It is important to recognize that our study is limited to a sample size of two plants, which implies the possibility of not recording the full diversity of potential seed dispersers.…”

“…All cone visitors recorded here are nocturnal animals, and the removal and dispersal of Ceratozamia norstogii seeds occur at night. Nocturnal seed dispersal has been observed in other cycads ( Hall and Walter 2013 , Yáñez-Espinosa et al 2021 Monteza-Moreno et al 2022 ), so it is likely that nocturnal dispersal is common amongst Ceratozamia species.…”

“…Some authors suggest that cycad species, in general, can be dispersed by rodents ( González-Christen 1990 , Yáñez-Espinosa et al 2021 ), birds ( Eckenwalder 1980 , Velazco-García et al 2016 ) and small and medium-sized mammals ( Pérez-Farrera and Vovides 2004 , Velazco-García et al 2016 , Monteza‐Moreno et al 2022 ). This seed-animal interaction could be unexpected in cycads because their seeds produce toxic substances (mainly methylazoxymethanol glycosides) that, when ingested, cause symptoms of poisoning in vertebrates ( Moretti et al 1983 , Hall and Walter 2014a ).…”