January 16January 16thth, 2007, 2007Antonia D’Amore, Antonia D’Amore,

Valentine Hemingway and Valentine Hemingway and Kerstin WassonKerstin Wasson

AQUATIC HABITAT AND LANDSCAPE AQUATIC HABITAT AND LANDSCAPE CHARACTERISTICS PREDICT DISTRIBUTION OF CHARACTERISTICS PREDICT DISTRIBUTION OF

AMPHIBIANS IN ELKHORN SLOUGHAMPHIBIANS IN ELKHORN SLOUGH

Main questions…• What predicts the distribution of pond-

breeding amphibians coastal California?

• Does the distribution of different species change significantly between years?

• How can we best manage to promote native amphibian populations?

• What are the threats to local populations?

Greg Hofmann

Rana draytonii – CA Red-legged frog

Largest native frog west of Rockies

Estimated to have been extirpated from 70% of historical habitat

Major threats include habitat destruction and degradation, invasive predators and potentially disease

Breed in December-April, tadpoles metamorphose by August

Adult red-legged frog

Rana catesbeiana – American Bullfrog

Largest frog in N. America

Native east of Rockies

Introduced for human consumption in the 1800s

Out-competes and eats native frog spp.

Thrives in human-modified habitat –perm. Ponds

Need year-round water to reproduce

Adult bullfrog

Psuedacris regilla – Pacific Tree Frog

Native to Western US and Canada

Most common amphibian from our surveys

Shorter larval period than other species

January DecemberAugust

Red-legged larval period – 4-7 months

Bullfrog larval period – 1 year

Pacific tree frog larval period – 2 months

Amphibian monitoring

Freshwater habitat in 5 mile radius around slough

Measured pond parameters

Habitat characteristics –spatial analyses

Presence/absence of different species

Water quality

Spatial analyses

Used GIS to look at spatial relationship between sites -- as well as threats

Distance to potential threats25m

130m

Distance to next site

What percentage of a 1 km buffer around the site is riparian habitat?agricultural?

Thanks Eric!

What do 3 years of monitoring data tell us?

Pacific tree frogs are more variable than other species

CA red-legged frogs breeding < 50% sites wherefound

Bullfrogs and Pacific tree frogs breed >90% sites where found

Most sites with CA red-legged frogs less than 20 individuals

Most sites in the watershed contain threats

What do we see when we look at species,site characteristics and annual patterns?

e.g. Do sites with roads within 50m have differentnumbers of adult frogs than sites without roads?

Red-legged patterns

1. All life stages negatively associated with roads

2. All life stages positively associated with ponds wet through August

3. Tadpole-juvenile found in warmer ponds

4. YOY-adult found in higher pH ponds5. Breeding found more in non-isolated

ponds

Within site characteristics + landscape level characteristics

Pacific tree frog patterns

1. Significant difference in number of sites with PTF between years (more in 2004 vs. 2005-6)

2. Negatively associated with both larger ranid species in wet years (2005 and 2006)

May be that when other breeding habitat is available, will choose not to breed in sites with other frog species

Environmental variation+

Species interactions

Bullfrog patterns

Far fewer determining factors emerge:

1. All life stages positively associated with ponds wet through August.

Highlights the management practice of seasonal dry-down for bullfrog control.

January DecemberAugust

Red-legged larval period – 4-7 months

Bullfrog larval period – 1 year

Pacific tree frog larval period – 2 months

What patterns do we find if we use all of the data together?

Broke data into two different matrices

amphibian data and environmental data

Multivariate statistics…

*** sites with and without red-legged frogs found

*** sites where they were found in zero, one, two or all three years

*** with/without red-legged breeding

BF and PTF no significant difference

Red-legged frog distribution – limited by environmental characteristics

Differences in environmental characteristics between sites with species as a factor? (ANOSIM)

What contributes to the differences we see between

sites?

nMDS

Do binary environmental factors drive community patterns? (ANOSIM)

Amphibian communities differ based on:

Ephemeral or permanent

With and without Gambusia spp.

Within 100m of a paved road or not

What variables best explain community pattern as a whole?

Link amphibian community data with environmental data

HydroperiodManmade/notWater temperatureSite isolation

BEST

Summary of findings

All three species are governed by different sets of requirements

California red-legged frogs have much more specific habitat requirements – less habitat available

Roads have a large impact on amphibian communities in our area

Managing hydroperiod -- control the spread of introduced bullfrogs