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

PASCUAL, J.; ALBERTI, J.; DALEO P; FANJUL, E.; ROCCA, C; IRIBARNE, O.

JOURNAL OF VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2019 vol. 20 p. 322 - 330

1100-9233

Question: Does the effect of droppings and herbivory by wild guinea pigs on saltmarsh vegetation vary across microhabitats?Location: Upper salt marsh in the Mar Chiquita coastal lagoon (37°44′52″ S, 57°26′6″W, Argentina).Methods: During autumn 2014, we performed a micro-scale experiment manipulating droppings of wild guinea pigs (Cavia aperea). After 15 days, we compared thecontent of nutrients (i.e., NH4+, NO3−, and PO43−) in soil. Then, we started two factorial experiments in the high marsh, specifically one in marsh matrix (i.e., tall vegetation) and the other in open patches (i.e., short vegetation). Units were randomlyassigned to different treatments (with and without herbivores and droppings). Inearly summer, we compared total plant cover, maximum height, above-ground biomass, plant species richness and the composition of plant assemblages betweentreatments.Results: Droppings increased the content of PO43− in soil by five times, but decreasedthe content of NO3−. Herbivory reduced total cover, plant height, and above-groundbiomass in the marsh matrix and the open patches. In the marsh matrix, droppingsincreased the total cover, whereas herbivory reduced the abundance of Spartina densiflora (cover and above-ground biomass) and subordinate species (cover). Additionally,the cover of subordinate species was negatively associated with the cover of Spartinadensiflora. Therefore, in the marsh matrix, by increasing light availability at the groundlevel, herbivory increased plant species richness, but with low cover of subordinatespecies. In contrast, in open patches, herbivory and droppings interacted to reduceplant species richness.Conclusion: Herbivory by small mammals can control the above-ground biomass,structure, and plant community composition of the high marsh, but non-trophicmechanisms (droppings) can also affect community composition. Nonetheless, ecological impacts of small mammals depend on the context, because the magnitude anddirection of trophic (herbivory) and non-trophic (droppings) effects change acrossmicrohabitats.