Population demographics influence genetic responses to fragmentation: A demogenetic assessment of the `one migrant per generation' rule of thumb
Authored by Lucas R Nathan, Yoichiro Kanno, Jason C Vokoun
Date Published: 2017
DOI: 10.1016/j.biocon.2017.02.043
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Abstract
Fragmented landscapes reduce gene flow and impair long term population
viability. Stream networks are particularly susceptible to fragmentation
because dispersal is constrained to linear upstream and downstream
movements. Despite these potential effects, infrequent migrations can
maintain genetic diversity and as few as one migrant per generation
(OMPG) is commonly suggested as sufficient gene flow to minimize losses
in genetic diversity. However, demography varies by taxa, space and
time, making such a generalized rule of thumb unlikely to be applicable
across a diverse array of fragmentation scenarios and species. We
utilized a demogenetic model to evaluate the OMPG rule and simulate the
influence of population demographics on the rate of genetic changes
following fragmentation in a headwater meta-population of brook trout
(Salvelinus fontinalis). A single migrant per generation increased
allelic diversity by an average of 15\% and decreased genetic
differentiation by 31\% following 40 years of simulations compared to
complete isolation, however OMPG was not sufficient to prevent
significant changes in within- or between-population genetic metrics in
all but the largest population scenario (N = 500). Less than 10
individuals were typically required to achieve no changes in both
genetic metrics, yet this pattern was dependent on the source
populations and will be context specific given the population
sub-structuring in a given stream network. Sensitivity analyses
indicated the parameter controlling the proportion of mature females
spawning annually was the most influential on population genetic
responses in isolated populations, suggesting that when fewer females
contribute to each generation the population is more likely to
experience rapid changes in allelic frequency through genetic drift.
This finding supports the use of metrics such as effective population
size and the number of effective breeders in predicting population
stability and viability following fragmentation. Variability in
population dynamic processes and associated responses to fragmentation
suggest that generalized rule of thumbs for management should be used
with caution. Particularly when violations of the underlying theoretical
assumptions exist, consideration of demographic processes (i.e. vital
rates, species specific life history strategies and dispersal) and
genetic structuring will allow for more appropriate conservation
recommendations.
Tags
Individual-based model
Habitat fragmentation
Dispersal
landscape genetics
Fragmentation
Barriers
Life-history
Brown trout
Brook trout
Trout salvelinus-fontinalis
Conservation genetics
Gene
flow
Subdivided populations
Stream
fish
Demogenetics
Stream networks