Species-based conservation Flashcards
What are the different approaches to conservation?
- Species-based
- Landscape-scale conservation
- Ex-situ conservation
Step-by-step of conservation process
- Assess species e.g. IUCN Redlist
- e.g. Island foxes of California
- Unique subspecies on each island
- Populations declined by 90-99% in 1990s - Create species management plans
Listed as endangered in 2004, leading to management plan:
- identify threats: immigration of golden eagles, feral pigs, absence of bald eagles, canine distemper outbreak
- work with multiple stakeholders to implement plan - Implement plan:
- relocated golden eagles back to mainland
- eradicate feral pigs (food per eagles)
- reintroduce bald eagles (exclude golden eagles)
- captive breeding & release foxes
- vaccination against distemper - Continue monitoring
- one of the fastest recoveries of any mammal
- due to: use of science & data, multiple organisations working together, presence of intact habitat
What are the problems with small populations?
- Stochasticity
- Low effective population size (Ne)
- Low genetic diversity
What is stochasticity and what is it vulnerable to?
- random variation in birth and death rates
- changes in sex ratio
- diseases
- disasters
- extreme weather conditions
What is low effective population size (Ne), why is it smaller, and what does it lead to?
Effective population size (number of individuals that contribute genes equally to the next generation) = always lower than census size
smaller due to:
-age distribution (many individuals may be immature)
- unequal sex ratio
- reproductive skew (unequal breeding success)
- bottlenecks & founder events
Low effective population size leads to loss of genetic diversity
Low genetic diversity
- genetic drift - more likely in small populations
- inbreeding - causes reduced fitness (inbreeding depression)
Where does avoiding extinction vortex usually focus on and why?
small populations, prone to extinction vortexes
e.g. Alee effects - evolutionary fitness of individuals decreases at low population sizes
Step by step process that leads to extinction
- Small population
- inbreeding, genetic drift
- loss of genetic variability
- reduction in individual fitness and population adaptability (and human impacts, demographic stochasticity, environmental stochasticity)
- high mortality, low reproduction
- smaller population
- extinction
What measure can tell us how long we can go?
Minimum viable population (MVP) sizes
What do the cross-species studies show about MVPs?
show that MVPs for 90% chance of population survival are usually 3000-5000 individuals
Examples of MVPs
e.g. bighorn sheep
120 populations monitored
all unmanaged populations of <50 individuals went extinct within 50 years
Why can sizes be much lower for some popuations?
- many species live in fragmented populations so sizes are much lower
- e.g. half of 23 isolated elephants populations of west Africa have fewer than 200 individuals
- Total population = around 7,745 individuals
What is essential for conservation of species?
habitat corridors
How do we measure population sizes?
census - count of number of individuals
- e.g. BTO Breeding bird Survey
- 3000 volunteers, allocated 1km2 square to survey each spring
- record birds seen/heard
Capture-mark recapture
- capture, mark, release
- later date, recapture same population
- more recaptures with marks, lower the population size likely
Genetics
- can use to conduct census where you can’t count individuals
- can calculate Ne directly using genetic data
Disadvantage of census to measure population sizes?
- time-consuming
- some species hard to detect
- often not repeated over time
