Seasonal patterns of endozoochory by cattle in subtropical grassland in southern Brazil

Abstract

Seed dispersal influences plant community dynamics and regeneration. Zoochory by cattle is a particularly important type of dispersal in grasslands, but still poorly understood in subtropical grasslands. We studied endozoochory in a native grassland area with different grazing intensities, defined by distinct forage allowance levels. On one day in each of the four seasons of the year, dung samples were collected and kept in a greenhouse for germination over one full year. At each dung collection date, a survey of reproducing plants was conducted to relate the species composition of seed within dung to the community in dispersal phase. We used randomisation tests to compare grazing intensities and seasons in terms of dung community richness, abundance and composition. We recorded 93 species in the dung samples, with 65 species in the spring samples, 61 in summer samples, 45 in the autumn samples and 37 in the winter samples. Of the 90 species identified in the vegetation, almost 50% (43 species) also occurred in dung samples. Graminoid herbs presented the largest number of species in all samples. Grazing had no effect on overall seed and species number, but was related to compositional differences in the cattle dung communities. Grazing also influenced the species composition in relation to life cycle, by the increase of annual species at the extremes of our grazing gradient (very high or very low grazing intensities). We conclude that endozoochory by cattle is an important process for the dispersal of native species in the studied system, with potential applications in grassland management and restoration. A better understanding of the strategies involved in seed dispersal is essential to improve knowledge about grassland vegetation regeneration and maintenance.

Germinação, superação da dormência de sementes e dispersão endozoocórica por bovinos de espécies nativas de pastagens naturais

“…Os resultados encontrados no presente estudo indicam que os bovinos podem atuar como agentes de dispersão (Fazelian et al, 2014; Lisboa et al, 2009) e espalhar grandes volumes de sementes por longas distâncias (Janzen, 1984), superando a limitação de sementes em projetos de restauração (Silva & Overbeck, 2021), que pode ser mais limitante em pastagens nativas do que a competição ou a predação de sementes (Pinto et al, 2014). Além disso, dispersam as sementes na superfície do solo (banco de sementes do solo ‐ BSS).…”

“…No entanto, a endozoocoria requer a ingestão de sementes (Fazelian et al, 2014) que podem ser danificadas durante o processo de mastigação e ruminação (Alvarez et al, 2016), ou seja, as sementes passam por processos físico‐químicos que afetam sua recuperação e germinação (Milotić & Hoffmann, 2016; Wang et al, 2019). Assim, essa quantificação é útil para avaliar a ferramenta de restauração (Silva & Overbeck, 2021), e depois a germinação de sementes é essencial para o estabelecimento das mudas e o sucesso da restauração (Middleton et al, 2010).…”

Germination, overcoming seed dormancy and endozoochory dispersal by cattle of native species from natural grassland

“…However, endozoochory requires the ingestion of seeds (Fazelian et al, 2014) that can be damaged during the process of chewing and rumination (Alvarez et al, 2016), that is, the seeds undergo physical–chemical processes that affect their recovery and germination (Milotić & Hoffmann, 2016; Wang et al, 2019). Thus, considering that seed germination is essential in the establishment of seedlings (Middleton et al, 2010), quantifying the endozoochoric potential is a key tool in restoration processes (Silva & Overbeck, 2021).…”

“…Grasslands native species are not available in the seed market, restricting directed seeding (Andrade et al, 2015). In this sense, cattle can act as a seed dispersal agent (Silva & Overbeck, 2021; Traba et al, 2003) by the endozoochory mechanism, that is, by the ingestion and subsequent elimination in faeces, cattle may transport seeds (Albert et al, 2015). However, endozoochory requires the ingestion of seeds (Fazelian et al, 2014) that can be damaged during the process of chewing and rumination (Alvarez et al, 2016), that is, the seeds undergo physical–chemical processes that affect their recovery and germination (Milotić & Hoffmann, 2016; Wang et al, 2019).…”

Tree logs for grassland restoration? Lessons from an unintentional experiment

“…In grasslands, seed dispersal by animals also may play a role in restoration (see, e.g. Minervini Silva & Overbeck 2021 for the role of endozoochory), but perches should be less successful as few grassland plant species are dispersed by birds. The most common species in subtropical grassland belong to the Poaceae and Asteraceae (Andrade et al 2019), plant families that contain many species that exhibit anatomical adaptations in their diaspores that facilitate dispersion by wind or surface dispersal (e.g.…”