Download Managing Populations

Ch. 13: Managing
Populations
The Black Robin
• 1976: Only 7 individuals on a small island
• moved to bigger, more stable island (had been recently restored)
• continued to decline
• 1979: Only 5 individuals
• supplemental feeding
• removing eggs to be raised by other species
• black robins would then lay another clutch
• artificial nest boxes
• parasite and predator control
• At one point, only one female
• Now there are over 250
• Population management can work!
Management Techniques
• You need to know these for your term paper!
• Once problems are identified, we can try and mitigate them:
• providing scare resources (food, nesting sites, water)
• controlling or reducing threats (predators, habitat destruction,
invasives)
• direct manipulation of population (translocations, introductions)
Providing Resources: Food
• Supplemental feeding
• Providing carcasses free of poison or lead shot to CA condor
• Cultivating specific plants – nitrogen fixing, larval hosts
• salt licks to supplement salt and mineral needs
• Consequences of supplemental feeding
• animals become dependent
• concentrates animals, facilitates disease
• changes in timing of breeding, migration
• Manipulating light and nutrient levels for plants
• low nutrients may favor rare plants
Providing Resources: Water
• Water is a limiting factor, but don’t want to replace arid area
with a wetland.
• Arid-adapted species may be restricted to driest portion of
original range and/or competing with domesticated grazers.
Providing Resources: Structure
• Physical environment affects microclimate, provides
concealment or shelter, and substrate (especially important
for sessile organisms)
• Nest boxes for birds, bees, fish
• Artificial reefs
• Bat boxes
Providing Resources: Biotic Int.
• Some species rely on symbionts.
Must protect whatever species
your target species depends on.
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Prey or hosts
Pollinator
Nutrient cycling
Ecosystem engineer
• Social stimulation
• breeding colonies
Controlling Threats: Overexploitation
• Human population and the consumption and pollution that goes
with it is the primary threat.
• easier to manage at local scale than global
• Overexploitation hard to regulate
• endangered plants not given protection on private lands
• game wardens must work in remote areas, nearly everyone they
encounter is armed
• Supply and demand is working against us! Rarity increases price
• Additive vs. compensatory harvest mortality
• compensatory: does not increase natural population mortality (duck
hunting)
• additive: increases natural population mortality (sea turtle bycatch)
• Several ways to limit
• how much, who, when, where, how it is done
Controlling Threats: Indirect
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Most harm is unintentional
Provide wildlife crossings
Grates over bat caves to exclude people
Restricting boat speeds
Controlling Threats: Consumers
• Predators
• exotics: can decimate native populations
• native: increase in # due to anthropogenic foods, exert too much
predation
• may use direct killing, fencing, removal
• Herbivores
• more numerous than predators
• overgrazing may go unnoticed, but can cause trampling, erosion,
desertification, and affect primary production
• may be controlled with fencing, direct killing, removal, insecticides
• Parasites & Pathogens ~ Conservation medicine
• Avoid overcrowding, other stressors
• Vaccination
• Competitors
• weeding, prescribed fire, targeted killing, broad-scale poison
Direct Manipulations: Translocation
• Translocations: intentional movement to maintain biodiversity
• introductions: to sites where organism did not exist previously
• typically on small islands in archipelagos
• reintroductions: to sites where organism was extirpated
• 50% success rate
• augmentation: supplementing existing populations
• common for game and timber species, less so for listed ones
• risk introducing a disease, outbreeding depression
• occasionally to move unwanted individuals
• endangered plant on land slated for development
• release of exotic pets or over abundant natives
Direct Manipulations: Artificial Breeding
• Double-clutching: removing a clutch of eggs to induce a second
bout of laying
• only works for species who re-lay after nest depredation
• Cross-fostering: allowing foster parents to raise young
• when done by another species, possibility for confusion of crossfostered individuals
• Head-starting: interventions that increase the survival of young,
usually in species with no parental care
• Hatcheries
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typically for aquatic species
use same technology as farms, but then release into wild
can be a good tool, but a bad sign if we need to use it
lots of side effects ~ genetics, antibiotics, chemicals, feed
Maintaining Genetic Diversity
• Gene banking: like a seed bank, but for genes and not in the
ground, in a lab
• Best way: Maintain enough individuals from populations
across a species’ range and habitats
• Important considerations when manipulating populations
• ideally use genetically similar individuals, but what if there are
none?
• maximize outbreeding and let natural selection do the rest?
• pick the closest approximation?
• Minimizing inbreeding in isolated populations
• Removing individuals carrying defects or susceptible to
diseases before they can breed
Discussion Qs
• Killing natives to reduce competition with rarer native
species?
• Continue intensive management for species that could not
persist without continued human intervention? At what
monetary expense?
• Examples from you conservation success stories? Or failures?