Habitat engineering by an apex predator generates spatial trophic dynamics across a temporal environmental stress...

Area of Science:

• Ecology
• Ecosystem Dynamics
• Conservation Biology

Background:

• Ecosystem engineers, like American alligators, create habitats that influence species interactions and biodiversity.
• Alligator ponds serve as crucial dry-season refuges, offering opportunities to study ecological dynamics under stress.
• The stress-gradient hypothesis (SGH) and intermediate disturbance hypothesis (IDH) predict how species coexistence changes with environmental stress and disturbance.

Purpose of the Study:

• To test if alligator-engineered ponds facilitate species coexistence along a seasonal drying (stress) gradient.
• To investigate the effects of alligator ecosystem engineering on trophic dynamics and food-web structure.
• To evaluate predictions of the SGH and IDH using long-term data and detailed dietary analyses.

Main Methods:

• Modeled fish catch-per-unit-effort (CPUE) in ponds and marshes from 1997-2022.
• Analyzed stomach contents (n=1677) and stable isotopes (n=3978) of fish and other taxa (2018-2019).
• Quantified diets, trophic niche areas, trophic positions, and basal-resource use across habitats and seasons.

Main Results:

• Fish CPUE in alligator ponds increased 12-fold as marshes dried, confirming their role as refuges.
• 73% of diet shifts occurred in the dry season, with differing niche area changes between stomach contents and stable isotopes.
• Alligators ameliorated dry-season stress by engineering deep-water habitats and altering food-web dynamics.

Conclusions:

• Ecosystem engineers like alligators facilitate species coexistence, particularly at intermediate stress/disturbance levels.
• Alligator ponds demonstrate the importance of habitat engineering in maintaining biodiversity under environmental stress.
• Findings support the SGH and IDH, highlighting the role of engineers in mediating ecological dynamics.