Conserving Small Populations In-Situ Flashcards
what is stochasticity?
Random variation affecting populations, especially impactful when populations are small.
what are the two types of stochasticity?
Environmental stochasticity: Weather, disease, catastrophes.
Demographic stochasticity: Random variation in births, deaths, sex ratio.
what does conservation need to factor in?
Conservation needs to go beyond theory and factor in genetic, environmental, and demographic effects.
what is the logistic growth model
dN/dt = rN (K-N/K)
what are allee effects?
Reduced individual fitness at low population densities (Berec et al., 2006).
what are the two types of allee effects?
Component Allee Effects: Positive relationship between any fitness component (e.g., mating success) and density.
Demographic Allee Effects: Observed as hump-shaped per capita growth rate vs. density curves—strong evidence of underlying component effects.
what are strong vs. weak allee effects?
Strong: Growth rate becomes negative below a threshold = extinction likely.
Weak: Growth rate stays positive, but recovery is slow.
what is the allee threshold?
Allee Threshold: Population size below which extinction becomes inevitable.
what can multiple allee effects cause?
More than one Allee effect can occur simultaneously (Berec et al., 2006).
May cause “Dormant Allee Effects”: weak effects interact to produce a strong extinction threshold unexpectedly.
what are anthropogenic allee effects?
Rarity increases a species’ value (e.g., exotic pets, trophy hunting), accelerating decline.
what does exploitation and allee effects cause?
Exploitation + Allee Effect = Double Threat: Can push population below Allee threshold (Berec et al., 2006).
how do populations fluctuate in the real world?
Populations don’t follow theoretical models exactly.
K and r can change due to environmental events.
Small populations are vulnerable to natural catastrophes.
what is the extinction vortex?
Allee effects, low reproductive output, skewed sex ratios → population spirals toward extinction.
what are source-sink dynamics?
Viable populations (sources) help maintain populations in poorer habitats (sinks).
what is the example of High Brown Fritillary Butterfly and the conservation priorities?
~75% of populations showed Allee effects (Bonsall et al., 2014).
Low immigration + Allee effects = high extinction risk.
Habitat fragmentation: only 2–13% of potential dispersal links used.
Conservation priorities:
Boost habitat connectivity.
Improve quality of both occupied and unoccupied patches.
Maintain populations above Allee thresholds.
what is the example for Sinai Baton Blue (Hoyle & James, 2005)
World’s smallest butterfly; highly fragmented population.
Global warming: Small temp rises = big extinction risk.
Human pressure: Grazing & plant collection steadily degrade habitat.
Additive stressors: Climate + grazing = dramatically increased extinction probability.
Critical patches (A & B) essential for metapopulation survival.
how can exploitation affect populations with their allee thresholds and what are some examples?
Fishing, hunting, and collecting can push populations below Allee thresholds, hastening extinction (Berec et al., 2006).
Example:
Irish Sea skates and sharks: 4 species driven to extinction by bycatch alone.
what is the purpose of the population viability analysis and what does it incorporate?
Predicts extinction risk under different conditions.
Incorporates:
Demographic stochasticity
Genetic drift
Environmental variation
Catastrophes
what is the PVA model structure?
Nt+1 = Nt λ
what must conservation strategies do for conserving small populations in situ?
Identify and protect critical habitat patches.
Boost habitat connectivity to aid dispersal and counteract isolation (Bonsall et al., 2014).
Consider combined human and environmental threats (Hoyle & James, 2005).
Use PVA to assess and plan conservation under uncertainty.
