Influence of landscape Influence of landscape and reach-scale and reach-scale

variables on aquaticvariables on aquaticcommunity structure community structure

in tropical island in tropical island streamsstreams

Catherine L. Hein, Andrew S. Pike, J. Felipe Blanco, Todd A. Crowl, Fred N. Scatena,

Melinda Laituri, and Alan P. Covich

6 Native Fishes

Mullet Eels

Eleotrids Gobies

10 Native Shrimps and 1 River Crab

Palaemonid Shrimp

Atyid Shrimp

Tropical Island Streams

Larvae

AdultsPost-larvae

Eggs/Adults

Diadromy

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

4 pools/riffles at each of 24 sites

Espiritu Santo Mameyes

Physicalmodels

Social models

Biologicalmodels

Integratedmodels

Integrated framework

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 SamplingTrapping 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

– Length – Width– Variation in width– Maximum depth– Variation in depth

• Grain size– Bedrock – Megaboulder – Boulder – Cobble – Gravel – Sand – Fines

Atya lanipes

Vertical Drop > 3.5 m

Absent Present

Anguilla rostrata Gobiomorus dormitor

AbsentPresent

Agonostomus monticola

Individual Species Distributions – Waterfalls

No Yes

Elevation < 439 m

Absent Present

No Yes

Individual Species Distributions – Elevation

Macrobrachium carcinus

Elevation > 100 m

Absent

Present

No Yes

Elevation < 439 m

Absent

No Yes

Macrobrachium crenulatum

Individual Species Distributions – Pool Length

Pool length < 23 m

Absent Present

No Yes

Pool length> 28 m

Absent Present

No Yes

Xiphocaris elongata Awaous tajasica

Individual Species Distributions – Grain Size

Median grain size <64 mm

Absent Present

No Yes

Eleotris pisonis

% Fine sediment

< 0.004

Absent Present

No Yes

Sicydium plumieri

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?1. Metrics besides presence/absence were

not tested (e.g. abundance)

2. Diadromous fauna are resilient

Why do anthropogenic factors not have an effect on diadromous

fauna?

1. Metrics besides presence/absence were not tested (e.g. abundance)

2. Diadromous fauna are resilient

3. 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