Biodiversity and exotic species invasion in riparian plant communities

Biodiversity and exotic species invasion in riparian plant communities Rebecca Brown Eastern Washington University

Riparian Areas • Areas along rivers that are influenced by flooding • Uniquely connected habitat from upstream to downstream reaches and aquatic to terrestrial environments • Provide ecosystem services (wildlife habitat, erosion control, and water quality protection)

REALLY diverse! >180 plant species per 1000 m2 40 exotic plant species (introduced by people to habitats outside of their natural range)

Why are there so many native and exotic species in riparian areas?

Exotic Species • Threat to global biodiversity • Expensive to remove • Understanding what makes habitats susceptible to species invasion is one of the fundamental questions in ecology

Is invasibility related to diversity? “…the balance of relatively simple communities of plants and animals is more easily upset than that of richer ones; that is… more vulnerable to invasions” Charles S. Elton 1958

Is invasibility related to diversity? “…the balance of relatively simple communities of plants and animals is more easily upset than that of richer ones; that is… more vulnerable to invasions” Charles S. Elton 1958 But what about riparian plant communities?

Invasion Invasion Diversity Diversity The diversity-invasibility debate + - Mixed or no relationship Stohlgren and Chong 2002 Wiser et al. 1998 Bruno et al. 2002 Burger et al. 2001 Sax 2002 Lonsdale 1999 (mostly observational, large scale) Levine 2001 Lavorel et al. 1999. Brown and Fridley 2003 Duncan 1996 Stohlgren et al. 1998 Brown and Peet 2003 Prieur-Richard et al. 2000 Stachowitz et al. 2002 Dukes 2002 Tilman 1997 Hector et al. 2001 Knops et al. 1999 (mostly experimental, small scale)

Why care? Implications of diverse communities being resistant to exotic species invasion: • Loss of species diversity could cause more exotic species invasions • Argument for protecting seemingly unimportant species from extinction • Should diverse habitats be given priority for conservation?

PresentationOverview Why are there so many native and exotic species in riparian areas? How are diversity and invasibility related? • Conceptual framework - immigration hypothesis • What is the relationship between flooding, diversity, and invasion? • How does scale influence the relationship between diversity and invasibility in riparian areas? • What is the relationship between flooding and seed supply? • Do riparian zones have greater compositional similarity with distance due to high dispersal? • What implications does this have for the influence of dams on riparian plant communities?

The diversity of a plant community represents a balance between two distinct sets of processes: • Extinction processes • competition • environmental stress • extreme disturbance • predation • Limits species richness • (the number of species) • Immigration processes • seed inputs • moderate disturbance • net resource availability • Increase immigration of • native and exotic • species

Immigration processes in riparian areas: • Flood disturbance • Increased seed supply from flood waters • High net resource availability

Seed Supply Conceptual relationship between disturbance, seed supply, and species richness

0.1 m 1 m 0.31 m 3.1 m 10 m Methods • 107 100-m2 vegetation plots • Percent cover by species recorded • Environmental data collected for each plot • Multiscale data • 1075 upland plots from Carolina Vegetation Survey

Hupp and Osterkamp 1985 Methods107 riparian plots stratified by geomorphic position. Landforms sampled: • Bar • Floodplain • Terrace(s) • Upland

Bar Floodplain Terrace

Seed Supply Predicted position of geomorphic positions relative to immigration vs. extinction processes

Native Species Richness Over Four Landforms Native Species Richness per 100 m2 Bar Floodplain Terrace Upland n=35 n=56 n=16 n=1075 Floods often No floods

Native Species Richness per 100 m2 Bar Floodplain Terrace Upland n=35 n=56 n=16 n=1075 Native Species Richness Over Four Landforms A B B,C D Floods often No floods

A Exotic Species Richness per 100 m2 B C D Bar Floodplain Terrace Upland n=35 n=56 n=16 n=1075 Exotic Species Richness Over Four Landforms Floods often No floods

Spatial scale effects Small scales: Saturation, plant to plant competition = negative relationship Larger scales: Variation in other factors (disturbance, seed supply, fertility) = positive or no relationship

p < .001 Relationship between diversity and invasibility at different scales 2 100 m 40 30 Exotic species richness 20 10 0 0 20 40 60 80 100 Native species richness

p < .001 p = 0.001 Relationship between diversity and invasibility at different scales 2 2 1 m 100 m 4 40 3 30 2 Exotic species richness 20 1 10 0 0 0 20 40 60 80 100 0 5 10 15 20 Native species richness

p < .001 p = 0.001 NS Relationship between diversity and invasibility at different scales 2 2 2 1 m 0.1 m 100 m 3 4 40 3 30 2 2 Exotic species richness 20 1 1 10 0 0 0 0 2 4 6 8 10 0 20 40 60 80 100 0 5 10 15 20 Native species richness

p < .001 p = 0.001 p = 0.02 NS Relationship between diversity and invasibility at different scales 2 2 2 2 1 m 0.1 m 100 m 0.01 m 3 3 4 40 3 30 2 2 2 Exotic species richness 20 1 1 1 10 0 0 0 0 0 2 4 6 8 10 0 1 2 3 4 5 0 20 40 60 80 100 0 5 10 15 20 Native species richness

Seed supply: The richness and abundance of seeds arriving at a site

131 seed traps placed near vegetation plots Seeds collected 6 times over 3 years Clay pads measure natural supply rates (don’t trap seeds) Seed source not limited to flooding Measuring seed supply

Seed germination

No flood Flood No flood Flood Seed Diversity and Abundance in Flooded and Unflooded Seed Traps Chi2= 7.00, df = 1, P = 0.008 Chi2= 4.45, df = 1, P = 0.035

1 High dispersal Similarity Low dispersal 0 Distance Distance Decay of Similarity

Measuring Similarity • Sorensen similarity = 2a / (2a + b + c) • a = shared species • b = species in group 1 but not group 2 • c = species in group 2 but not group 1

Measuring Similarity • Calculate Sorensen similarity between every possible pair of plots in each geomorphic position • Compare distance decay of similarity for each geomorphic position

Distance decay of similarity for 3 rivers

Does this indicate higher dispersal in flooded sites? • Possibly... Alternative explanation: • Flooded sites might have more homogeneous environmental conditions at the scales represented here than upland sites

Summary of Results • Diversity and invasion increase with increased flooding • The relationship between native and exotic species richness was positive at large scales and negative at small scales • Seed supply was higher in flooded areas • Riparian areas have higher compositional similarity with distance than uplands

Why are there so many native and exotic species in riparian areas? • Riparian areas are immigration-driven because of flooding which creates disturbance and increases seed supply and resource availability • This promotes high numbers of both native and exotic species

How are diversity and invasibility related? Depends on the degree to which the community is immigration- or extinction- driven - and spatial scale • Positive relationship in immigration-driven communities sampled at large spatial scales • Negative relationship in extinction-driven communities or when sampling occurs at very small scales relative to the size of the plants

Broader Implications • In extinction-driven communities, the loss of species diversity could potentially permit more invasions • This is not the case, however, for all communities (such as riparian zones) • Invasibility depends on more than the number of species

Dam impacts that may affect riparian plant communities Upstream Impoundment Downstream • Inundate riparian vegetation • Fragment riparian zone • Trap seeds • Store water and sediment • Reduced seed supply • Altered flood regime • Reduced sediment supply • Disturbed riparian habitat • Reduce or eliminate marine derived nutrients from migratory fish

Biodiversity and exotic species invasion in riparian plant communities

Biodiversity and exotic species invasion in riparian plant communities

Presentation Transcript

Exotic species

Exotic and Invasive Species

wild species and biodiversity

Pathogens and Plant Invasion Ecology

Species Diversity in Communities

Biodiversity and Invasion

Wild Species and Biodiversity

Exotic species

Invasive and Exotic Species

Invasion of the Species

Invasive/Exotic Species

SPECIES BIODIVERSITY

Exotic and Invasive Species

Biodiversity within plant based communities

Exotic Species

Biodiversity – Factors Exotic Species Mongoose Predator in Hawaii

Exotic Herbivore Species Grazing Effect On Plant Life

Biodiversity – Factors Exotic Species Species invasions may profoundly affect ecosystems

Biodiversity and species

Communities biodiversity, issues keystone species habitats, niches Interactions:

Biodiversity and Endangered Species