Influence of landscape and reach-scale variables on aquatic community structure in tropical island streams Catherine L. Hein, Andrew S. Pike, J. Felipe Blanco, Todd A. Crowl, Fred N. Scatena, Melinda Laituri, and Alan P. Covich

6 Native Fishes Eels Mullet Eleotrids Gobies

10 Native Shrimps and 1 River Crab Palaemonid Shrimp Atyid Shrimp

Tropical Island Streams Diadromy Larvae Eggs/Adults Post-larvae Adults

Modeling Complex Interactions of Overlapping River and Road Networks in a Changing Landscape Overarching hypothesis: An integrated, individual based modeling framework will better predict interactive effects of humans on river landscapes than will individual physical, chemical, biological and social models

Sample Sites Espiritu Santo Mameyes 4 pools/riffles at each of 24 sites

Integrated framework Social models Physical models Biological models

What natural and anthropogenic variables at landscape and/or reach-scales determine fish and decapod community structure in two Puerto Rican watersheds? Distribution of each species (6 fishes and 8 decapods) Community assemblage

Field Sampling Trapping Snorkeling Electrofishing Sampled 90 pools and associated riffles

Landscape Variables Largest downstream vertical drop (m) Elevation % land cover within a 250 m radius of each site (urban, agriculture, or forest) Number of downstream road crossings Road type

Geomorphology Pool Variables Grain size Length Width Variation in width Maximum depth Variation in depth Grain size Bedrock Megaboulder Boulder Cobble Gravel Sand Fines

Individual Species Distributions – Waterfalls Vertical Drop > 3.5 m No Yes Atya lanipes Absent Present Anguilla rostrata Gobiomorus dormitor Absent Present Agonostomus monticola

Individual Species Distributions – Elevation Macrobrachium carcinus Elevation > 100 m Absent Present No Yes < 439 m Macrobrachium crenulatum Elevation < 439 m No Yes Absent Present

Individual Species Distributions – Pool Length Xiphocaris elongata Awaous tajasica Pool length < 23 m Pool length > 28 m No Yes No Yes Absent Present Absent Present

Individual Species Distributions – Grain Size Eleotris pisonis Sicydium plumieri % Fine sediment < 0.004 Median grain size <64 mm No Yes No Yes Absent Present Absent Present

Community Assemblage

Community Assemblage Headwaters Ocean Large circles indicate greater decapod species richness

Conclusions Natural landscape-level barriers are largely responsible for patterns in community structure Fishes are below waterfalls and most decapods are above

Conclusions Roads, dams, and urban and agricultural land covers do not significantly affect species distributions in these watersheds Why not?

Culverts Bridge piles Narrow squared culvert Large bridge

Why do anthropogenic factors not have an effect on diadromous fauna in the Espίritu Santo and Mameyes watersheds? Metrics besides presence/absence were not tested (e.g. abundance) Diadromous fauna are resilient

Why do anthropogenic factors not have an effect on diadromous fauna? Metrics besides presence/absence were not tested (e.g. abundance) Diadromous fauna are resilient Chronic changes to the landscape have not yet occurred

High Head Dams & Exotic Species

Acknowledgements Dave Kikkert Ruth Kikkert Maria Ocasio Torres Enrique Marrero Coralys Ortiz Andy Crowl Paul Nicholson Kaua Friola Wyatt Cross Chelse Prather Funded by NSF