Role of small rodents in the seed dispersal process: Microcavia australis consuming Prosopis flexuosa fruits

Abstract

Understanding the functional role of animal species in seed dispersal is central to determining how biotic interactions could be affected by anthropogenic drivers. In the Monte Desert, mammals play different functional roles in Prosopis flexuosa seed dispersal, acting as opportunistic frugivores (endozoochorous mediumsized and large mammals) or seed hoarders (some small sigmodontine rodents). Our objective was assessing the functional role of Microcavia australis, a small hystricognathi rodent, in the fruit removal and seed deposition stages of P. flexuosa seed dispersal, compared to sympatric sigmodontine rodents. In situ, we quantified fruit removal by small rodents during non-fruiting and fruiting periods, and determined the distance seeds were transported, particularly by M. australis. In laboratory experiments, we analysed how M. australis stores seeds (through scatter-or larder-hoarding) and how many seeds are left in caches as living seeds, relative to previous data on sigmodontine rodents. To conduct field studies, we established sampling stations under randomly chosen P. flexuosa trees at theÑacuñ an Man and Biosphere Reserve. We analysed fruit removal by small rodents and seed dispersal distance by M. australis using camera traps focused on P. flexuosa fruits covered with wire screen, which only allowed entry of small animals. In laboratory trials, we provided animals with a known number of fruits and assessed seed conditions after removal. Small rodents removed 75.7% of fruit supplied during the non-fruiting period and 53.2% during the fruiting period. Microcavia australis and Graomys griseoflavus were the main fruit removers. Microcavia australis transported seeds to a mean distance of 462 cm and cached seeds mainly in scatter-hoards, similarly as Eligmodontia typus. All transported seeds were left in fruit segments or covered only by the endocarp, never as predated seeds. Microcavia australis disperses P. flexuosa seeds by carrying fruits away from a source to consume them and then by scatter-hoarding fruits and seeds.Results of Wald test using Microcavia australis as intercept are shown. Significant results (P < 0.05) are indicated in bold. Data on sigmodontine rodents are from Giannoni et al. (2013).

Duality of interaction outcomes in a plant–frugivore multilayer network

“…Assessing the viability of seeds collected from small mammal feces is extremely difficult (see different approaches in Traveset and Verdú , Traveset et al , Sahley et al , Campos et al ). The tetrazolium test used here, which has largely been used in agriculture rather than in community ecology, is an efficient tool to access an important component of seed dispersal quality (Schupp et al ).…”

Small mammal abundance and seed predation across boundaries in a restored‐grazed woodland interface

“…The seed predation exerted by small rodents in the PRA would contrast with the surrounding grazing sites if we considered the fact that other mammal species such as Microcavia australis and Dolichotis patagonum, regarded as more efficient Prosopis seed dispersers (Campos & Ojeda 1997;Campos et al 2017), could find more suitable habitats in areas under grazing (Tabeni & Ojeda 2005). Contrary to small mammal preferences, these medium-sized mammals prefer more open habitats (Tognelli et al 1995;Corbalán & Ojeda 2004).…”

Studying the quantity component of seed dispersal effectiveness from exclosure treatments and camera trapping

“…Microcavia australis , which is larger than 100 g, was able to access the “open to small mammals” exclosure. As this species has a different functional role in seed dispersal than small mammals <100 g, which are mainly seed predators (Giannoni et al., ), using the exclosures alone would have overestimated the contribution of small mammals to seed predation and underestimated seed dispersal by scatter‐hoarding mechanisms (Campos et al., ).…”

“…Some medium‐sized mammals (weight greater than 3 kg) act as opportunistic frugivores that disperse seeds through endozoochory, such as Dolichotis patagonum (mara; Rodentia: Caviidae), Lagostomus maximus (plains viscacha; Rodentia: Chinchillidae), Lycalopex griseus (Argentine gray fox; Carnivora: Canidae), and the exotic Lepus europaeus (European hare; Lagomorpha: Leporidae) (Campos & Ojeda, ). Rodent species can also behave as scatter‐hoarding seed dispersers, such as Microcavia australis (southern cavy; Rodentia: Caviidae; weight 200–300 g; Campos et al., ) and as larder‐hoarding seed predators ( Graomys griseoflavus and Akodon dolores ) (gray leaf‐eared mouse and grass mouse; Rodentia: Cricetidae; weight less than 100 g; Giannoni et al., ). Also other species were recorded removing P. flexuosa fruits, such as Zaedyus pichiy (pichi; Cingulata: Chlamyphoridae), Conepatus chinga (Molina's hog‐nosed skunk; Carnivora: Mephitidae), Ctenomys mendocinus (Mendoza tuco‐tuco; Rodentia: Ctenomyidae), and Thylamys pallidior (pallid fat‐tailed opossum; Didelphimorphia: Didelphidae), but their roles in the seed dispersal process remain unknown (Campos et al., ).…”

“…Considering functional groups as sets of species showing similar effects on major ecosystem processes (Gitay & Noble, ), the following functional groups were defined based on previous studies (Campos & Ojeda, ; Campos & Velez, ; Campos et al., , ; Giannoni et al., ): “opportunistic frugivores,” “scatter‐hoarders,” and “seed predators.” Species with as yet unknown functional roles were grouped as “others.”…”