Metapopulations in conservation (was: Checkerspot in the news)

[John Shuey]

Here's a long train of thought on a new twist to this old thread.  I'm
looking for feedback and ideas that might help refine this approach to
conservation.

niklas.wahlberg at helsinki.fi wrote (in part):

>  ....  Nevertheless, I think that the concept of metapopulations has
> brought
> much to conservation. A good rule of thumb is that suitable habitat that
> does not have a certain species is as important as habitat that does
> have the species. We've been studying a relative of E. editha, Melitaea
> cinxia, for the past 7 years here in Finland. In a patch network of
> several thousand suitable habitat patches there have been several
> hundred local populations each year. All but a handful have gone extinct
> _at least_ once during the study period ....

Indeed, metapopulations theory permeates almost everything we do (at TNC) in
the Midwestern US, where because of habitat conversion to agriculture,
almost all native species survive as "artificial metapopulations".  By
framing our efforts in light of metapopulations, and designing reserves that
can seeming accommodate metapopulation function, we believe that we can
maximize conservation at our sites.

Almost by definition, classic metapopulations are inherently unstable,
subject to stochastic variables likely to result in local population
extinctions.  All else being equally between two species, a species with a
true metapopulations structure is harder to conserve than a species that
grades toward patchiness.  Almost every action that you can take to enhance
metapopulation function should enhance viability of other types of
populations (with exceptions for disease and outbreeding depression -
neither of which have been an issue at sites I'm familiar with).  Thus said
(and assuming that its actually true), a conservative approach towards
conservation is to accommodate metapopulations at conservation sites.  The
down side is that we know nothing about population structure of  most
species at sites, which can range from flies that form leaf galls, to plants
that require specific pollinators.

So, we develop strategies that should generically influence two portions of
metapop equations.   First, we address habitat patch size (which should
correlate to population size for most targets, hence influencing the
probability of extinction).  Second, we attempt to increase the
re-colonization rate between habitat patches, such that at minimum,
emigration between patches equally local extinction (preferably it swamps
the local extinction rate - and you end up with 75% or greater patch
occupancy).  We usually do this by looking at the spatial distribution of
habitat patches.

Seems simple enough, so here are two examples from NW Indiana, originally
dominated by mesic prairie with oak savanna scattered on sand ridges. This
region has been almost completely converted to row-crop agriculture (>95% in
some counties).  Wildfire originally maintained open grasslands and savanna
- but now our surviving ecosystem remnants are fire suppressed and and
densely shaded (unless they are already managed for biodiversity).

Example 1.  Jasper County.  Extensive oak savanna remnants persist on
glacial outwash, isolated by a sea of agriculture.  Our approach here is two
phased.  First we (and the the State of Indiana) have acquired  the largest
and best of these remnants, and are aggressively restoring open savanna
conditions (70% canopy removal combined with Rx fire).  We now have series
of habitat islands ranging in size from 500-1,000 acres, but separated by up
4 miles of inhospitable land.  These initial sites were chosen because (on a
relative scale) they still maintained significant portions of their native
biota.  The sites offer internal redundancy of ecotones and micro-habitats
and are large enough to accommodate a conservation fire rotation.
Basically, they are the best sites for "stand-alone preserves".

    But, they are still stand-alone preserves, supporting at best, poorly
functional metapopulations, or more likely isolated populations. Thus, we
have decided to build a better archipelago, and we are now acquiring and
restoring degraded "stepping stone"  savannas will that bridge the gaps.
These will include tiny remnants that by themselves, we would never have
considered viable (e.g. as small as 40 acres).  Our goal is to reduce the
maximum distance between high-quality savanna patches to 0.5 miles, with the
average distance being more like 0.3 miles. I think that this will enhance
viability of the entire system for the long-term  -  allowing  species that
are absent from key sites, to re-colonize the larger preserve on their own
(in essence, we hope to re-create conditions that will allow metapopulations
to function over this landscape).  Implementation will require about 1,000
acres of additional land, and with initial restoration, total costs of this
additional effort will run about US$3M.

Example 2.  Newton County Sand Prairies and Savannas.  This site is very
similar to previous example, except that two species of  prairie did not get
plowed under.  One of these (just across the state line in Illinois) is
2,400 acres, and is probably viable as a stand-alone site.  The other is a
640 acre wet to dry sand prairie, that is situated between two savanna
remnants, each about two miles away.  Here we have decided to re-create a
contiguous landscape (largely because of the rarity of the sand prairie
habitat and the species it supports).  Thus we purchased 7,000 acres of
row-crop farmland that physically connects, the prairie with these two
savanna remnants.  Our goal here is actually to destroy "artificial"
metapopulation structure as best as possible, creating instead a series of
patchy populations that occupy about 15 square miles of grassland / savanna
habitat.  The restoration is designed to maximize internal ecological
redundancy and complexity, such that once it becomes fully integrated into
the natural system (maybe in 100 years or so), populations of native
grassland species will find their "natural" structure at the site.  The cost
of this effort will be about US$20M.

Conservation was a lot cheaper before metapopulations were "discovered".

Note that these examples are both grand experiments.  We are in the process
of developing "tools" to assess our ability to expand populations of
conservative insects at these sites, but for the vast majority of species,
we will likely never know if or how we influenced their persistence in these
systems.  But based on my current train of thought, these seem like
reasonable strategies, likely to produce positive results.



--
John Shuey
Director of Conservation Science
Indiana Office of The Nature Conservancy

phone:  317-923-7547
fax:  317-923-7582
email:  Jshuey at tnc.org