Prather herbivore and detritivore effects on plant biomass

Consumer effects on rainforest primary production are often
considered negligible because herbivores and macro-detritivores usually consume
a small fraction of annual plant and litter production, even though consumers
are known to have effects on plant production and composition in non-tropical
systems. Disturbances, such as tree fall gaps, however, often increase
resources to understory food webs, thereby increasing herbivory and feeding
rates of detritivores. This increase in consumption could lead to more
prominent ecosystem-level effects of consumers after disturbances, such as
storms that cause light gaps. We determined how the effects of invertebrate
herbivores (walking sticks) and detritivores (litter snails) on understory
plant growth may be altered by disturbances in a Puerto Rican rainforest using
an enclosure experiment. Consumers had significant effects on plant growth, but
only in light gaps. Specifically, herbivores increased plant growth by 60%, and
there was a trend for detritivores to reduce plant growth. Additionally, plant
biomass tended to be 50% higher with both consumers in combination, suggesting
that herbivores may mediate the effects of detritivores by altering the
resources available to detritivore food webs. This study demonstrates disturbance alters the
effects of rainforest consumers, and, furthermore, that consumer activity has
the potential to change rainforest successional processes.