Animals connect plant species and resources in a meta-ecosystem

Abstract

Context

Movement of individuals and resources among habitat patches are key processes at the landscape scale. While these subsidies are primarily studied separately, coupled movement of species and resources, for example by animal vectors, may reinforce or dilute natural landscape heterogeneity, with consequences for the spatial distribution of biodiversity.

Objectives

We examine how transport of nutrients and seed by consumers’ feces corresponds to productivity gradients in the landscape, and whether herbivores and carnivores differ in the types of seeds they transport.

Methods

In California, we surveyed fecal deposition by vertebrates in 10 serpentine grassland fragments of varying productivities. We analyzed nitrogen content of feces before performing a germination assay to identify species transported therein.

Results

Herbivores deposited substantial amounts of nitrogen in serpentine grasslands via their feces, while carnivore scat was a high-quality but less predictable resource subsidy. Neither trophic group’s fecal deposition reinforced or diluted productivity gradients in the landscape. Rather, unproductive fragments received minimal nutrients, while more productive fragments had the chance of receiving higher resource inputs. Feces from both types of consumers contained viable seeds, but herbivores and carnivores transported non-overlapping subsets of plant species.

Conclusions

Consumers play different roles connecting plant communities in the landscape according to trophic level. Small herbivores are a continuous source of nutrient cycling, and their feces contains serpentine-adapted plant species, potentially serving as vectors for stepping-stone dispersal. While carnivores may be important vectors for long-distance seed dispersal, their movement patterns also make them more likely to deposit seeds in unsuitable environments.