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Killer whales and sea otters

Killer whales and sea otters. Daily caloric requirements:. Male killer whale: 308,000 Kcal/day or 5-7 sea otters. Killer whale and seal otter energetics. Female killer whale: 187,000 Kcal/day or 3-5 sea otters. Account for 40,000 sea otters lost over 6 years?.

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Killer whales and sea otters

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  1. Killer whales and sea otters • Daily caloric requirements: • Male killer whale: 308,000 Kcal/day or 5-7 sea otters • Killer whale and seal otter energetics • Female killer whale: 187,000 Kcal/day or 3-5 sea otters • Account for 40,000 sea otters lost over 6 years? • 5 sea otters per day per whale x 365 days x 6 years = 10,950 sea otters! • 10,950 sea otters eaten x 4 whales would account for 40,000 sea otter losses Where have all the sea otters gone?

  2. Killer whales and sea otters • Sea otters usually not main component of killer whale diet -- why the change? • Some fish populations have declined in recent decades • Shortage of certain fish caused substantial declines in harbor seals and sea lions • Shortage of seals and sea lions resulted in killer whales preying on smaller sea otters Where have all the sea otters gone?

  3. Sea otters important part of coastal community; loss of sea otters results in many indirect effects Killer whales and sea otters • Why should we care about sea otter declines? Where have all the sea otters gone?

  4. Indirect effects on communities • Predation (or parasitism) can reduce competition, preventing competitive exclusion • Predators typically feed on several types of prey • Prey selected based on its relative abundance • Superior competitors can reach high relative abundance, but predation can control such populations • Example: removal of starfish (Pisaster) in rocky intertidal results in competitive exclusion by mussels Where have all the sea otters gone?

  5. Indirect effects on communities • Predation (or parasitism) can result in many indirect effects on other species • Example: ant-rodent interactions • Both ants and rodents eat seeds in Chihuahuan Desert • Removal of rodents caused initial increase in ant populations, but then a decrease Where have all the sea otters gone?

  6. Indirect effects on communities • Keystonespecies = species that have strong effect on the composition of the community • Removal of keystone species causes a decrease in species richness • Example: sea otters eat sea urchins which are superior competitors; if sea urchin populations increase, kelp reduced and species richness drops Where have all the sea otters gone?

  7. Indirect effects on communities • Kelp ‘forest’ Where have all the sea otters gone?

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