12/2/2011 1 Dispersal What is it? Intergenerational movement (Kenward et al 2002) Permanent movement of an individual from place of birth to place of reproduction (Howard 1960) Natal dispersal : movement from nest (birth) site to site of 1st reproduction Breeding dispersal: movement between breeding locations (Greenwood and Harvey 1982) Methods of Studying Dispersal Markers: Passive: paint, colorbands, tattoos, etc Active: PIT tags, GPS-collars, VHF radios Genetic: Fst Populations with > F st are less genetically similar, suggesting lower rates of successful dispersal than those with < F st Others? Maximum dispersal distance experiments12/2/2011 2 The nature of passive versus active markers can yield a different picture of the dispersal process: Importance/Roles of Dispersal: Thoughts? Persistence of species locally and rangewide Metapopulation theory – rescue, recolonization sources and sinks Expansion of range – new colonization and establishment current issues that make this important? Genetically - maintenance / source of genetic variation within and between species Reducing competition locally (density dependent disp.)12/2/2011 3 Marti (1999) Studied Barn Owls in N. Utah from 1977-1996, following nests and using passing markers (colorbands) to follow individuals. Based on his results, what is the general pattern for dispersal distances? Do there appear to be differences in dispersal patterns between male and female Barn Owls? Females disperse farther on average than males. Possible ecological explanations for this?12/2/2011 4 How about directionality of dispersal? Estimating dispersal distances from telemetry data. What constitutes dispersal? A set movement distance ? A set time out of home range core?12/2/2011 5 Estimating dispersal distances from telemetry data. Can get direction and rate of movement Can build utilization distribution and link to landcover/habitat information to build a resource utilization function to understand how habitat variables influence movement rates, stop times, etc. Whittaker and Marzluff 2009) Golden-Cheeked Warbler (Dendroica chrysoparia) • breeds in closed-canopy woodlands, primarily Ashe juniper and oak • declined due to habitat loss and fragmentation from clearing of juniper for urban expansion, agriculture, and commercial harvest12/2/2011 6 Modeling Different Dispersal Scenarios in Golden-cheeked Warblers Scenario Description NoD No dispersal SymD 15% symmetric dispersal SurvD 15% symmetric dispersal; disperser survival declines with distance KD Excess individuals above K become dispersers KSurvD Same as KD; disperser survival declines with distance KSurvDVitals Same as KSurvD; Larger pops. have higher survival and fecundity (Horne et al. 2011) Used stochastic, demographic based modeling approach to determine effect of these scenarios on metapopulation mean final abundance (mfa), and ran sensitivity analyses for each scenario to determine most important demographic
View Full Document
Unlocking...