predation. effects of predation on morphology, distribution and abundance 1.change in size structure...
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Predation
Effects of predation on morphology, distribution and
abundance
Effects of predation on morphology, distribution and
abundance1. Change in size structure of prey population (if predator prefers the largest individuals in a prey population)
1. Change in size structure of prey population (if predator prefers the largest individuals in a prey population)
Brooks and Dodson 1965 (over 1350 citations)Brooks and Dodson 1965 (over 1350 citations)
Lakes in North AmericaWhen fish were introduced there were huge changes- predators preferred the larger zooplankton- small zooplankton became dominant- large phytoplankton become abundant
Lakes in North AmericaWhen fish were introduced there were huge changes- predators preferred the larger zooplankton- small zooplankton became dominant- large phytoplankton become abundant
Effects of predation on morphology, distribution and
abundance
Effects of predation on morphology, distribution and
abundance2. Decreases in overall diversity – if predators are very efficient at removing prey, they drive populations to extinction which reduces diversity
3. 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
2. Decreases in overall diversity – if predators are very efficient at removing prey, they drive populations to extinction which reduces diversity
3. 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
Effects of predation on morphology, distribution and
abundance
Effects of predation on morphology, distribution and
abundance4. Morphological modifications – inference from
observationa. protective devices (spines on sea urchins; strong shells)
4. Morphological modifications – inference from observationa. protective devices (spines on sea urchins; strong shells)
Effects of predation on morphology, distribution and
abundance
Effects of predation on morphology, distribution and
abundance4. Morphological modifications – inference from observation
b. mimicry – organisms that resemble unpalatable species (usually because they contain toxic compounds)
4. Morphological modifications – inference from observation
b. mimicry – organisms that resemble unpalatable species (usually because they contain toxic compounds)
Effects of predation on morphology, distribution and
abundance
Effects of predation on morphology, distribution and
abundance4. Morphological modifications – inference from
observationc. crypsis – organisms match the color and shading of their habitats. This morphology is likely shaped by predatory pressure over time.
4. Morphological modifications – inference from observationc. crypsis – organisms match the color and shading of their habitats. This morphology is likely shaped by predatory pressure over time.
Artificial camouflageDecorator crabs put algae on their backs, which increases their survival
In areas with Dictyota spp. (algae), crabs use this species for decoration, but rarely food
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.
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.
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
• 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 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
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 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• When the keystone sea otter is removed, sea
urchins overgraze kelp and destroy the kelp forest
Figure 5.15b
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