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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. • • • • 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 • • • • 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 • • • • 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?