Primer of Conservation Genetics:
Take Home Messages
Throughout the book we focus on a number of primary
concepts that define the core of conservation genetics. At the end of
the book we have included a final section summarizing these main messages:
-
The biological diversity of the planet
is rapidly being depleted due
to direct and indirect consequences of human activities (habitat
destruction and fragmentation, over-exploitation, pollution and
movement of species into new locations). These reduce population
sizes to the point where additional stochastic (chance) events (demographic,
environmental, genetic and catastrophic) drive them
towards extinction.
-
Genetic concerns in conservation biology arise from the deleterious
effects of small population size and from population fragmentation
in threatened species.
-
The major genetic concerns are loss of genetic diversity, the
deleterious
impacts of inbreeding on reproduction and survival, chance
effects overriding natural selection and genetic adaptation
to
captivity.
-
In addition, molecular genetic analyses contribute to conservation
by aiding the detection of illegal hunting and trade, by
resolving
taxonomic uncertainties and by providing essential information
on little-known aspects of species biology.
-
Inbreeding and loss of genetic diversity are inevitable
in all small
closed populations and threatened species have, by
definition,
small and/or declining populations.
-
Loss of genetic diversity reduces the ability
of populations to
adapt in response to environmental change (evolutionary
potential).
Quantitative genetic variation for reproductive
fitness is the
primary component of genetic diversity involved.
-
Inbreeding has deleterious effects on reproduction
and survival
(inbreeding depression) in almost every naturally
outbreeding
species that has been adequately investigated.
-
Genetic factors generally contribute to
extinction risk, sometimes
having major impacts on persistence.
-
Inbreeding and loss of genetic diversity
depend on the genetically
effective population size (Ne), rather
than on the census size (N).
-
The effective population size
is generally much less than the
census
size in unmanaged populations,
often only one-tenth.
-
Effective population sizes
much greater than 50 (N > 500)
are
required to avoid inbreeding
depression and Ne = 500--5000
(N =
5000--50 000) are required
to retain evolutionary potential.
Many
wild and captive populations
are too small to avoid inbreeding
depression and loss of genetic
diversity in the medium term.
-
The objective of genetic
management is to preserve
threatened
species as dynamic entities
capable of adapting to
environmental
change.
-
Ignoring genetic
issues in the management
of threatened
species
will often lead to
sub-optimal management
and in some
cases to
disastrous decisions.
-
The first step
in genetic management
of
a threatened
species is
to resolve any
taxonomic uncertainties
and
to delineate
management
units within
species. Genetic
analyses
can aid in resolving
these issues.
-
Genetic management
of species
in nature is in
its
infancy.
-
The greatest
unmet
challenge in conservation
genetics
is to
manage
fragmented
populations
to minimize
inbreeding
depression
and loss
of genetic
diversity.
Translocations
among
isolated
fragments
or creation
of corridors
for
gene
flow
are required
to minimize
extinction
risks,
but they
are
being
implemented
in
very
few cases.
Care
must
be taken
to avoid
mixing
of
different
species,
sub-species
or populations
adapted
to different
environments,
as
such
outbreeding
may have
deleterious
effects
on reproduction
and survival.
-
Genetic
factors
represent
only
one
component of
extinction
risk.
The
combined
impacts
of
all ‘non-genetic’ and
genetic
threats
faced
by
populations
can
be
assessed
using
population
viability
analysis
(PVA).
PVA
is
also
used
to
evaluate
alternative
management
option
to
recover
threatened
species,
and
as
a
research
tool.
-
Captive breeding
provides a
means for
conserving species
that are
incapable
of surviving
in their
natural habitats.
Captive populations
of
threatened species
are typically
managed to
retain 90%
of
their
genetic diversity
for 100
years, using
minimization of
kinship.
Captive
populations may
be used
to provide
individuals for
reintroduction
into the
wild.
-
Genetic deterioration
in captivity
resulting from
inbreeding depression,
loss
of genetic
diversity and
genetic adaptation
to captivity
reduces
the probability
of successfully
reintroducing species
to
the wild.
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