Once upon a time, population planning in zoos was largely a local affair.
Zoos focused on their own animals, the emphasis was on producing offspring
to attract visitors and even threatened or endangered species rarely had
plans in place to maximize the health of the entire captive population. This
view changed over time as zoos became more conservation-minded, but even as
recently as 2000, breeding plans were still the province of dedicated zoo
professionals belonging to the Small Population Management Advisory Group
(SPMAG) who volunteered their time to make breeding recommendations.
In a bid to formalize population planning (and take some of the stress off
SPMAG volunteers), the Association of Zoos and Aquariums (AZA) founded the
Population Management Center (PMC) in June 2000. Housed at Lincoln Park Zoo,
the PMC is dedicated to providing scientific guidance for the care and
breeding of more than 100 essential Species Survival Plan (SSP) and
Population Management Plan (PMP) species at more than 200 member zoos.
Working with funding split between the AZA and Lincoln Park Zoo (Brookfield
Zoo was an original partner but has since left the program), three full-time
staff members—Population Biologists Sarah Long and Colleen Lynch and
Studbook Analyst Louise Bier—analyze family trees in order to find the best
genetic matches for managed species. This scientific planning helps to
maintain the genetic diversity found in the wild while also ensuring that
zoos have the animals they need now and in the future for conservation and
education purposes.
The planning is always growing. Since its inception, the PMC, instituted
with a generous gift from John Alexander, has steadily expanded to include
more animals and more partners. Whereas the Center worked with 28 species in
its first year, it covered 61 in 2005, and in its six-year history has
produced 268 plans for 153 species while working with nearly every zoo in
the AZA. “In the beginning, people didn’t know what to expect,” explains
Long, “but now that they’ve seen how it works, they’re more eager to
collaborate with us. We like to see our role as being an advisor, helping
management programs make the best decisions. In the end, everyone
contributes to the ultimate goal, which is managing our populations to
ensure they’re as healthy as possible.”
While the science behind their planning is sound, the execution can be
difficult, as the following reasons illustrate.
Good Genes Wanted
“Breeding isn’t always the desired outcome for PMC recommendations,” says
Lynch. In fact, the majority of the time animals receive the recommendation
not to breed as a result of PMC analysis. Specific reasons for the cold
shower can include overrepresented genes or space concerns, but the
underlying rationale is the long-term viability of the species.
Animals most likely to receive breeding recommendations are those with genes
that are underrepresented in the population. Captive populations are
typically a closed gene pool; few new animals are introduced, meaning as
time passes, an increasing proportion of the population may be descended
from just a few founders. By examining studbooks—collections of the family
trees of each animal in the population, detailing how many offspring they’ve
had and with whom—PMC planners can favor genetic lines that are
underrepresented in the population while ensuring that animals that are
overrepresented take a break from breeding. This task is assisted by
population-management software designed by Lincoln Park Zoo that ranks every
individual’s genetic makeup on a scale ranging from rare (underrepresented)
to least rare (overrepresented). Ideally, sound management will result in
each genetic lineage being equally represented in the population.
An example of successful planning can be seen with the pheasant pigeon. Zoos
across the country hold 49 members of this rain forest species, while the
PMP’s objective is to raise that number to 100. Lincoln Park Zoo took a step
towards this goal in March when a chick was born to a founder pheasant
pigeon, one with genes previously unrepresented in the captive population.
This successful breeding will ultimately increase the genetic diversity of
the population as a whole.
Space Matters
Despite their conservation goals, zoos ultimately have a finite amount of
space, which offers another check on breeding. In addition to using genetic
analyses to preserve genetic diversity, the PMC also has to perform
demographic evaluations looking at a population’s size and age distribution
in order to aid space planning. “Very large animals or animals that require
special care aren’t an option for every zoo,” explains Long. “One example is
polar bears—they’re a popular animal, but they also need a very specialized
space. Our planning has to ensure their population doesn’t exceed the
available space while also keeping room for rehabilitation animals that may
come in from the wild.”
Because of these constraints, polar bears are on a maintenance schedule,
meaning breeding only occurs to replace animals that pass away. This
planning has its challenges. If zoos simply halt breeding for a period of
time, they run the risk of the population being too old to reproduce when
it’s time for breeding to resume. Instead, regular births have to be plotted
in a way that keeps the population viable without exceeding the available
space. “You always want room to keep breeding,” says Lynch. “A start-stop
cycle can be very disruptive.”
Space concerns are often alleviated by housing multiple species in one
exhibit (not a recommended option for polar bears) or by forming nonbreeding
groups. This latter option can be seen with the chimpanzees at Lincoln Park
Zoo. The members of the group at Regenstein Center for African Apes have an
unsure genetic lineage—breeding wasn’t monitored at their previous
institution—and there are currently 300 chimpanzees in North American zoos,
as many as the available space can handle. PMC analysis resulted in a
no-breed recommendation from the Chimpanzee SSP, and the males in the group
were vasectomized in order to remove any breeding concerns. Lincoln Park Zoo
can thus care for the animals and provide the public with educational
opportunities while reserving breeding for more genetically underrepresented
animals.
Everyone Wants Newborns
The recommendation to prevent breeding can be a difficult one for many
institutions, as visitors are always interested in viewing new offspring.
The importance of the PMC is that it gives zoos an impartial mechanism
allowing them to pool resources to emphasize the long-term viability of a
captive species. “Our population planning can only work because of the
incredible cooperation we receive from zoos across the country,” says Long. “We try to reward this cooperation by spreading breeding opportunities
around so that sooner or later nearly every institution may be able to
breed.”
Institutions can also help manage expectations by educating visitors about
the importance of population management. Everyone enjoys seeing zoo
newborns, but guests can also appreciate that animals might help their
populations most by not breeding. In any case, breeding isn’t the only
measure of worth; nonbreeding animals still provide visitors with
opportunities for learning and wonder.
Even when breeding recommendations are made, attraction isn’t always a
matter of genetics. Sometimes the most desirable breeding animals just
aren’t compatible, making flexibility on the part of the PMC another
necessary trait. For every pairing, individual keepers and studbook managers
provide feedback to Long, Lynch and Bier; if offspring haven’t been produced
after a couple years, animals may be reassigned to try to find more
compatible partners. “Our planning is always ongoing,” says Lynch.
This constant planning enhances the well-being of thousands of animals at
hundreds of zoos across the United States. By using
sound scientific management to guide the breeding of more than
100 zoo species, the PMC and its numerous partners across the country are
working to ensure the viability of captive populations for generations to
come. 
