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Predation . Lakes in North America When fish were introduced there were huge changes - predators preferred the larger zooplankton small zooplankton became dominant large phytoplankton become abundant. Brooks and Dodson 1965 (over 1350 citations).

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slide2

Lakes in North America

  • When fish were introduced there were huge changes
  • - predators preferred the larger zooplankton
  • small zooplankton became dominant
  • large phytoplankton become abundant

Brooks and Dodson 1965(over 1350 citations)

Effects of predation on morphology, distribution and abundance

  • Change in size structure of prey population
  • (if predator prefers the largest individuals in a prey population)
slide3

Effects of predation on morphology, distribution and abundance

  • Decreases in overall diversity – if predators are very efficient at removing prey, they drive populations to extinction which reduces diversity
  • Increase in diversity– in simple systems with few prey species, one of which is a dominant competitor. If a predator prefers the dominant competitor it can reduce the number of the dominant competitors, allowing the inferior competitors to exist.
  • All three of these can occur in “ecological time” = one to a few generations
slide4

Effects of predation on morphology, distribution and abundance

  • Morphological modifications – inference from observation
  • a. protective devices (spines on sea urchins; strong shells)
slide5

Effects of predation on morphology, distribution and abundance

  • Morphological modifications – inference from observation
  • b. mimicry – organisms that resemble unpalatable species (usually because they contain toxic compounds)
slide6

Effects of predation on morphology, distribution and abundance

  • Morphological modifications – inference from observation
  • c. crypsis – organisms match the color and shading of their habitats. This morphology is likely shaped by predatory pressure over time.
slide7

Artificial camouflage

  • Decorator crabs put algae on their backs, which increases their survival
  • In areas with Dictyotaspp. (algae), crabs use this species for decoration, but rarely food
slide8

Inducible versus Constitutive defenses

A bryozoan makes spines when placed in contact with a predatory nudibranch.

A hydrozoan, Hydractinia, produces defense stolons armed with nematocysts when in contact with another colony.

slide9

Inducible Defense:

The conical (right) and bent (left) forms of the acorn barnacle Chthamalus anisopoma. The animal develops the bent form if predatory snails are present.

slide10

Mytilus edulis (Blue mussel)

Threat of predation leads to:

  • Thicker shells
      • Leonard et al (1999)
      • Smith & Jennings (2000)
  • Larger adductor muscle
      • Reimer & Tedengren (1996)
  • Increased gonad ratios
      • Reimer (1999)
  • Increased byssus volume
      • Cote (1995)
predation indirect effects
Predation: Indirect Effects

Non-lethal effects

Injury by browsing predators

Trait-mediated indirect interactive effects (TMII)

Risk averse foraging

More shelter dwelling in the presence of predators

Can produce larger effects than consumption does

Trophic cascades

predation indirect effects1
Predation: Indirect Effects

Non-lethal effects

Injury by browsing predators

Trait-mediated indirect effects (TMII)

Risk averse foraging

More shelter dwelling in the presence of predators

Can produce more dramatic effects than actual predation does

Trophic cascades

slide14

Dugongs can modify the structure of seagrass beds through their foraging

Tiger sharks cause dugongs to change habitats, which can affect seagrass communities

predation indirect effects2
Predation: Indirect Effects

Non-lethal effects

Injury by browsing predators

Trait-mediated indirect effects (TMII)

Risk averse foraging

More shelter dwelling in the presence of predators

Can produce more dramatic effects than actual predation does

Trophic cascades

trophic cascade in kelp forests
Trophic Cascade in Kelp Forests

When the keystone sea otter is removed, sea urchins overgraze kelp and destroy the kelp forest

Figure 5.15b

emergent multiple predator effects mpes
Emergent Multiple Predator Effects (MPEs)

Types of interactions among predators (Soluk and Collins, 1988):

Neutral: predators do not affect one another’s rates of prey consumption

Negative (interference): combined prey consumption less than neutral values  MPE

Positive (facilitation): combined prey consumption greater than neutral values  MPE