Herbivory and dropping effects by small mammals on salt marsh vegetation varies across microhabitats

PASCUAL JESUS; ALBERTI JUAN; DALEO PEDRO; FANJUL EUGENIA; ROCCA CAMILA; IRIBARNE OSCAR

JOURNAL OF VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2019

1100-9233

Question:Does the effect of droppings and herbivory by wild guinea pigs on salt-marshvegetation vary across microhabitats?Location: Upper saltmarsh in the Mar Chiquita coastal lagoon (37º 44´ 52´´ S, 57º 26´ 6´´W, Argentina).Methods:During autumn 2014, we performed a micro-scale experiment manipulatingdroppings of wild guinea pigs (Cavia aperea). After 15 days, we compared the content of nutrients (i.e. NH+4, NO3-, and PO43-) in soil. Then, we started two field experiments in the high marsh, specifically one in marsh matrix (i.e. tall vegetation) and the other in open patches (i.e. short vegetation). In both experiments, units were randomly assigned to different treatments: ?control with droppings?, ?control without droppings?, ?exclusion with droppings?, and ?exclusion without droppings?. After eight months (early summer), we compared the following measurements between treatments: total plant cover, maximumheight, above-ground biomass, plant species richness and the composition of plant assemblagesResults: Our results show that droppings increased by five times the content of PO43- in soil, but decreased the content of NO3-. Herbivory reduced total cover, plant height, and above-ground biomass in both the marsh matrix and the open patches. Particularly, in the marsh matrix fresh droppings increased the total cover, whereas herbivory reduced the abundance of S. densiflora (cover and above-ground biomass) and subordinate species (cover). In addition, the cover of subordinate species was a negatively associated with the cover of S. densiflora. Therefore, in the marsh matrix, by increasing light availability at the ground level herbivory increased plant species richness, but with low cover of subordinate species. In contrast, in open patches herbivory and droppings interacted to reduce plant species richness.Conclusion: Our study shows that small mammals can control the above-ground biomass, structure, and plant community composition of the high marsh mainly through herbivory, but our results show that non-trophic effects such as droppings can also affect community composition. Nonetheless ecological impacts of small mammals depend on the context, because the magnitude and direction of both trophic (herbivory) and non-trophic (droppings) effects change across microhabitats.