Movement and population dynamics of Harris' and Baltimore checkerspot butterflies.

Collaborators: Elizabeth Crone, Paul Severns, Sharon Stichter

The tiny butterfly to the left is a uniquely marked (two green dots were added with a metallic gel pen) Harris' Checkerspot. This butterfly is declining in New England, probably due to climate change (see next section). Conveniently, the species forms small discrete colonies and is ideal for mark-recapture designs to understand dispersal and meta-population dynamics, and the state's strongest populations are mostly all within a 10 minute drive of Harvard Forest. Given these facts we started a pilot mark-recapture population study around Harvard Forest to see if a longer term study might be feasible and worth while this past spring (2011).

We also started pilot projects on the Baltimore checkerspot (left). This butterfly has been experiencing a major population boom in New England, and anecdotal reports suggest this is due to the relatively recent evolution of the ability to utilitize a weedy invasive host (Plantgo lancelota). Prior to acquiring this ability, this species was declining and restricted by the patchy distribution of its single native host plant Chelone glabra (white turtlehead). In fact, this situation is still the case over most of its geographic range east of the Mississippi River. Some populations in New England still use the native host, but many now appear to be surviving on the invasive Plantago. It is not clear if these populations are exchanging individuals, or if the movement behaviour of adults is affected by the host plant each population uses. All else being equal, Plantago using populations should be more apt to disperse because the host plant is much more widespread and thus suitable patches much closer together and easier to find. So we hope to understand how individuals move between populations and at the edge of suitable patches relative to the host used at each patch.

In this pilot year, we've identified 3 field sites, each with a different host plant situation, measured movement with GPS tracking and mark-recapture, investigated adult host plant preference, investigated larval growth with common garden growth experiments on pre-diapause larval using different host plants, and surveyed pre- and post diapause larvae distributions at field sites. Much is left to be done, but the picture already emerging appears far more complex and interesting than we suspected. Stay tuned.

Climate Driven Community Changes in New England Butterflies

Collaborators: Elizabeth Crone, Sharon Stichter, Massachusetts Butterfly Club

Using a new modeling approach known as list-length analysis (Szabo et al. 2010, Ecology) designed for analysis of Citizen Science sightings data, I have been able to rigorously estimate the population trends for nearly all New England butterfly species present in Massachusetts. The data analyzed were gratiously provided by the Massachusetts Butterfly Club, who diligently collected, audited, and archived observations over the past 20 years. I cannot stress enough how helpful this organization has been and that my work could not have happened without the thousands of reports made by this dedicated group.

Above: The distribution of Atlantis fritillary (Speyeria atlantis) sightings in Massachusetts from 1992-2010. Size of circles indicates the number of individuals seen on a given day and the size is log scaled. Only two other species, the acadian hairstreak and aphrodite fritillary, are declining faster.

The results so far are stunning. They suggest rapid climate induced population declines in nearly all cold adapted species and numerous invasions from southern species that were previously unrecorded or only vagrants. The overall impression is of a wholesale northward shift of butterfly population ranges in eastern North America. A manuscript for these finding is nearly complete and will be submitted before Christmas 2011.

Above: Population trends for all butterfly populations in the state of Massachusetts with enough reliable sightings data to estimate trends. Estimates of change in detection probability that are positive indicate increasing populations, negative indicate decreasing populations.   We defined Northern species to have greater than 50% of their range north of the latitude of Boston, Southern species have ranges with greater then 50% of their range south of Boston. Cheat sheet for butterfly codes can be found here.

Movement Model Development

Observations and data from our field work have sparked development of a number of lines of theoretical and analytical model development. These include dynamic behavioural programming approaches to understand how female butterflies (or females of a wide range of other species) should allocate reporductive effort spatially. In this case, where should they deposit eggs given a particular spatial arrangement of patches or resources and the disturbance intervals, and how should this be balanced against dispersal. We predict that in increasingly patchy habitat, females should increase allocation (lay more eggs) in their natal patch. However, this behaviour is likely evolved, and species that evolved in a less patchy, more connected habitat may disperse before allocating much reproductive effort into a natal colony. Not allocating to the natal patch, and dispersing into habitat where the odds of locating another suitable patch are small will cause such an individual's fitness to decrease or go to zero. However, allocating more eggs to the single, natal patch is also not ideal, as it decreases the stability of the metapopulation network as that patch will eventually experience a catastrophic disturbance.

Finally, I am also developing models for understanding diffusion through habitats using mechanistic diffusion and CRW models to fit GPS tracking data from butterflies. These are being developed to understand the field data we collect.

Last update November 2011