AQUATIC HABITAT AND LANDSCAPE CHARACTERISTICS PREDICT DISTRIBUTION OF AMPHIBIANS IN ELKHORN SLOUGH. January 16 th, 2007

Transcription

1 AQUATIC HABITAT AND LANDSCAPE CHARACTERISTICS PREDICT DISTRIBUTION OF AMPHIBIANS IN ELKHORN SLOUGH January 16 th, 2007 Antonia D Amore, Valentine Hemingway and Kerstin Wasson

2 Main questions What predicts the distribution of pondbreeding 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?

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4 Greg Hofmann

5 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 Adult red-legged frog Breed in December- April, tadpoles metamorphose by August

6 Rana catesbeiana American Bullfrog Adult 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 humanmodified habitat perm. Ponds Need year-round water to reproduce

7 Psuedacris regilla Pacific Tree Frog Native to Western US and Canada Most common amphibian from our surveys Shorter larval period than other species

8 January August December Red-legged larval period 4-7 months Bullfrog larval period 1 year Pacific tree frog larval period 2 months

9 Amphibian monitoring Freshwater habitat in 5 mile radius around slough Measured pond parameters Habitat characteristics spatial analyses Presence/absence of different species Water quality

10 Spatial analyses Used GIS to look at spatial relationship between sites -- as well as threats 130m Distance to next site 25m Distance to potential threats

11 What percentage of a 1 km buffer around the site is riparian habitat? agricultural? Thanks Eric!

12 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 where found 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

13 What do we see when we look at species, site characteristics and annual patterns? e.g. Do sites with roads within 50m have different numbers of adult frogs than sites without roads?

14 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 ponds 5. Breeding found more in non-isolated ponds Within site characteristics + landscape level characteristics

15 Pacific tree frog patterns 1. Significant difference in number of sites with PTF between years (more in 2004 vs ) 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

16 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.

17 January August December Red-legged larval period 4-7 months Bullfrog larval period 1 year Pacific tree frog larval period 2 months

18 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

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

20 What contributes to the differences we see between sites?

21 nmds

22 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

23 What variables best explain community pattern as a whole? Link amphibian community data with environmental data BEST Hydroperiod Manmade/not Water temperature Site isolation

24 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

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