Lecture 9: Species-based Conservation Flashcards
What is species-based conservation ?
E.g.
- Sustainable harvesting (overexploitation)
- Assisted migration (climate change)
- Building evolutionary resilience (climate change)
Where do we start?
- Assess species e.g. IUCN Redlist
E.g. Island foxes of California, unique subspecies on each island, popualtions declined by 90-99% in 1990s. - Create species management plans
E.g. the foxes listed as endangered in 2004, leading to management plan: a) identify threats: immigration of golden eagles (from mainland), feral pigs, absence of bald eagles (compete with golden eagles), canine distemper outbreak (disease outbreak). b) work with multiple stakeholders to implement a plan to increase numbers again. - Implement plan
- Relocated golden eagles back to mainland.
- Eradicate feral pigs (food for eagles).
- Reintroduce bald eagles (exclude golden eagles) - Continue monitoring
- Kept monitoring foxes and was one of fastest recoveries of any mammal.
Due to: use of science & data, multiple organisations working together, presence of intact habitat.
(Can be more complex if lost habitat)
Problems with small populations: Stochasticity
Stochasticity (random/unpredictable events): Random variation in birth and death rates, changes in sex ratio, diseases, disasters, extreme weather conditions.
Problems with small populations: Low effective popualtion size
Effective population size: number of individuals that contribute genes equally to next generation. Is always lower than the census size (actual number of individuals there).
Made smaller due to:
- Age distribution (many individuals may be immature so cannot pass genes on yet)
- Unequal sex ratio (different number of males & females reduces number of individuals contributing to next generation) (e.g. 50 males and 50 females = theoretically can have census population size that matches effective population size, as move from 50/50 sex ratio, effective population size reduces)
- Reproductive skew (unequal breeding success) (e.g. elephant seals, small number of males that dominating reproduction, so small number of males contributing genes to next generation).
- Bottlenecks (population undergoes drastic reduction in size due to natural disaster or human intervention, can lead to loss of genetic variation or extinction) & founder (small group of individuals from a larger population establishes a new population in different geographic area/ habitat, may have reduced genetic variation compared to original population) events.
Problems with small populations: Low effective population size
- Leads to loss of genetic diversity.
- Smaller population leads to a loss more rapidly.
Problems with small populations: Low genetic diversity
- Genetic drift (changes in frequency of alleles due to chance) - more likely in small populations to loose alleles.
- Inbreeding - causes reduced fitness (inbreeding depression). (E.g. isle royale wolf population in US Great Lakes, only has immigrants when lakes freeze over which doesn’t happen very often anymore, so few individuals immigrate to population, led to skeletal deformation etc).
Avoiding the extinction vortex
- These things all together (small population, inbreeding, genetic drift = loss of genetic variation, reduce individual fitness & population adaptability, stochastic events can occur & human impacts, lead to high mortality & low reproduction then even smaller population and extinction) create extinction vortex’s.
- Related to alee effects - evolutionary fitness of individuals decreases at low population sizes).
How low can we go?
- Minimum viable population (MVP) sizes (population sizes needed to avoid extinction).
- Can try calculate it.
- Cross-species studies show that MVPs for 90% chance of population survival for 100 years usually between 3000-5000 individuals. If goal is 90% chance of survival for 1000 years the requirement is 100,000 individuals.
How low can we go?
- E.g. MVPs of bighorn sheep, 120 populations with limited dispersal between them. Found that if population was unmanaged & had population of <50 individuals then populations went extinct within 50 years. If had over 100 individuals then very few went extinct. To persist in longer term need to increase population size further.
How low can we go?
- Many species live in fragmented populations (smaller, isolated groups) so sizes are much lower.
- E.g. half of 23 isolated elephant populations of west Africa have fewer than 200 individuals, total population = ~7,745 individuals. Habitat corridors are essential. (Without causing human wildlife conflict).
How do we measure popualtion sizes?
Cenus - count of number of individuals.
- e.g. BTO Breeding bird survey, 3000 volunteers, each allocated 1 km squared of map to survey each spring and record birds they see/hear.
BUT
- time-consuming
- some species hard to detect
- often not repeated over time
How do we measure popualtion sizes?
Capture-mark recapture
- capture individual, mark them, release again
- capture from the same population at a later date
- the more recaptures that have marks, the lower population likely to be
How do we measure popualtion sizes?
Genetics
- can use to conduct a census where you can’t count individuals
- can calculate effective population size directly using genetic data
- e.g. dog trained to sniff out killer whale faeces, extract DNA & look whether male or female and construct a unique genetic profile for that individual, once have lots of samples can count effective population size.
Effective conservation requires knowledge of the species
- Concepts so far are broad and rough estimate.
Know about: - reproduction - when & where? Do we conserve nesting sites? E.g. leadbeaters possum need cavity’s in old trees to reproduce, main threat to breeding coming from wild fires & logging (removes larger trees that more likely to have breeding cavities). If didnt reduce high probability of going extinct.
- Timing of harvests for exploited species (don’t harvest when about to breed)
Effective conservation requires knowledge of the species
Habitat selection & requirements
- e.g. the wandering elephants of china in 2021
- came from a reserve and were trying to migrate, looking for other resources
- conservation measures (had been successful) led to increased populations & less elephant food in protected areas.
