Download - Checkerspot Butterfly Presentation
Euphydryas editha bayensis: Evidence for a Metapopulation ModelHarrison et al. 1998
http://www.calacademy.org/science_now/headline_science/
AM. NAT. 1988. VOL. 132, PP. 360-382.
Preliminary indications of Metapop. dynamicsFrequent Extinction of Local Populations
Behavior and patchiness limits recolonization
* Goal: To determine the extent, dynamics, and equilibrium of the potential metapopulation*
Life CycleAdults appear in March/April, eggs hatch in 2-3 weeks
Plantago erecta ,Orthocarpus sp.
Larvae enter summer diapause in May, ends in late fall
Larvae feed from Dec-Feb and pupate
http://plants.usda.gov/java/largeImage?imageID=pler3_003_ahp.tif
http://www.laspilitas.com/nature-of-california/plants/orthocarpus-densiflorus
http://www.botany.hawaii.edu/Faculty/Carr/ofp/images2/lom_mac_9347b.jpg
http://plants.usda.gov/java/profile?symbol=LACAC2&photoID=lach3_001_ahp.tif
http://www.americanmeadows.com/WildflowerSeeds/Species/TidyTipsseeds.aspx
http://calphotos.berkeley.edu/cgi/img_query?
query_src=&enlarge=6105+1651+0932+0099
“TIDY TIPS”
“FALSE BABYSTARS”
“BIGSEED BISCUITROOT”
“GOLDFIELDS”
Habitat Distribution- 15 x 30 kmNorthwest= San Jose
Northeast= Inner Coast Range
Southwest= Santa Cruz Mountains
GOOGLE MAPS
Habitat Quality
Steep southern/southwestern slopes are very different from northern/northeastern slopes
in most years, S/SW slopes contribute little to future pop size
in unusually wet years, S/SW slopes contribute disproportionately to future pop size
Density of plant sources vary from patch to patch
History of Extinction
“50 year drought”
Severe drought: 1975-1977
3 pops in the MH area went extinct
MH patch pop size likely extremely reduced (not likely to have gone extinct)
Pops observed in 1986 likely due to 9yr recolonization
Methods
Determined number of pops, potential habitat
patches with host plants= potential (59 total)
patches with adults= “occupied”
8 sites found in 1986 were checked for larvae
Methods, ctd.
Measure habitat quality
distance from MH, % warm, moderate, and cool slopes
topography
density indices (%s) for both host and 1 nectar plant
Logistic Regression (P<0.10)
Methods, ctd.
Estimation of population sizes found extant in 1986 and 1987
7 total
Mark-recapture
Regression of pop size and patch area
Regression to separate effect of distance from MH on patch quality
Results- Distance and Quality
All patches found in ’87 were 1.4-4.4 km from MH
Patch area did not affect plant density
All 6 variables significant in explaining presence/absence of butterflies (p< 0.10)
REGRESSION EXPRESSION FOR PRESENCE/ABSENCE VS DISTANCE AND QUALITY
Results- Pop. Sizes
Log(patch area) is a significant predictor of Log(pop size)
ln(warm area) was a significant predictor of pop size
Results- Quality
Of all the patches that were examined (59), using the quality formula (below), 27 were considered “suitable”
Discussion
Likelihood of patch occupancy depends on distance from MH and quality
GOOD ENOUGH, NEAR ENOUGH
NOT GOOD ENOUGH, TOO
FAR AWAY
NOT GOOD ENOUGH,
NEAR ENOUGH
GOOD ENOUGH, TOO FAR AWAY
Annual rates of colonization as a function of distance
I= probability (per unit time) of colonization
D= distance from source to target
D’= species-specific dispersal constant (estimated from data)
The radius of the MH metapopulation is estimated to be 7-8 km
“Stepping-Stone” colonizationIn some populations, emigration is higher at low population sizes
Colonization from several small patches could be important
Use a modified immigration function to model (immigration from MH + immigration from all occupied small patches)
Stepping stone islands unlikely to increase immigration rates to distant patches
Continuous ExtinctionAre extinctions due to a major, devastating event or factors affecting local populations
Data from Jasper Ridge indicate that mean time to extinction depends on log(initial pop size)
reciprocal is expected yearly probability of extinction and can be compared to expected yearly colonization rate
determined using 1987 observed (if available) and expected population sizes
Conclusions
MH metapopulation appears to be mainland-island
Habitat variables and distance from a source pop determine patch occupancy
Stepping stone colonization appears to be unimportant
Continuous and catastrophic extinctions occur