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

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

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-marsh vegetation vary across microhabitats?Location: Upper saltmarsh at the Mar Chiquita coastal lagoon (37º 44´ 52´´ S, 57º 26´ 6´´W, Argentina).Methods: During autumn 2014, we placed a micro-scale experiment manipulating droppings 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 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?. Eight months later, we compared between treatments: total plant cover, maximum height, above-ground biomass, plant species richness and the composition of plant assemblages. Results: Our results show that droppings increased five times the content of PO4 3- in soil beneath them, 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 herbivory reduced the abundance of S. densiflora (cover and above-ground biomass) and subordinated species (cover). In addition, the cover of subordinated species wasa 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 subordinated species. Contrary, in open patches herbivory and droppings interactively reduced plant species richness. Conclusion: Our study shows that small mammals can control the above-ground biomass, the structure, and plant composition of the high marsh mainly through herbivory, but our results show that non-trophic effects 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.