Food-web composition affects cross-ecosystem interactions and subsidies

Area of Science:

• Ecology
• Ecosystem Dynamics
• Food Web Interactions

Background:

• Ecosystems interact via species that cross boundaries and resource subsidies.
• Species identity influences the strength and nature of these cross-ecosystem effects.
• Terrestrial predators can influence aquatic communities and nutrient cycling.

Purpose of the Study:

• To investigate the effects of two terrestrial spider species on aquatic invertebrate communities.
• To determine the impact of these spiders on ecosystem processes like decomposition and nitrogen cycling.
• To understand how species identity and combined effects influence cross-ecosystem interactions.

Main Methods:

• Manipulation of two terrestrial bromeliad-living spider species (Aglaoctenus castaneus, Corinna gr. rubripes).
• Assessment of effects on aquatic invertebrate community structure (richness, abundance, biomass).
• Measurement of ecosystem processes: decomposition rate and nitrogen cycling.

Main Results:

• Aglaoctenus spiders reduced aquatic insect larvae, while Corinna spiders added nitrogen.
• Combined spider effects were generally the average of individual effects.
• Aquatic invertebrates with fully aquatic life cycles were unaffected or facilitated by spiders.
• Spiders did not alter detritivore biomass or detrital nitrogen flux.

Conclusions:

• Predators can reduce cross-ecosystem taxa while facilitating within-ecosystem taxa, potentially attenuating top-down effects.
• Species identity significantly impacts community structure and ecosystem functioning across ecosystems.
• The composition of both terrestrial and aquatic food webs influences cross-ecosystem interaction strength.