Predation and Herbivory Flashcards
1
Q
Predation and herbivory
A
- Predation: one animals eats another
- Herbivory: animal eats plant or algae
2
Q
What controls prey population?
A
Predators
-ex: Lynx and hares; when hare more abundant, so are lynx until lynx eats all the hares and starts to die off because not enough food…
3
Q
What controls plant population?
A
- Herbivores
- they can be used as biocontrol for ex: goats the keep competing vegetation
low between grape vines in vineyards - can alter physical environment
- ex: Beavers convert forest-bordered
streams into ponds and open meadows
4
Q
Predators shape ecosystems
A
- How? Extinctions, population declines, Yellowstone national park example with wolves
o Herbivory: deer eat aspen saplings, limit growth of forest
o Predation: wolves eat deer, limit growth of deer, increase growth of forest
-Also change behaviour of deer
5
Q
Predation
A
- Prey must avoid being eaten as much as possible or they will go extinct
- Predators must keep up with prey so as to be able to eat
6
Q
Predator avoidance: Early detection
A
- Prey can often detect predators first
• Ex: moths can usually detect bats first; have two pairs of ears (A1 and A2); A1 sensitive to low intensity sound, moth is further away than bat’s detection zone; bat detects moths at ~8m, moth detects bat ~100m; moth acts to avoid detection; how to moths know the bats location? Bat approaching: sound becomes louder and whichever side its approaching from will fire faster (A1 or A2) - A2 sensitive to loud sounds; so if A2 activated then bat has probably already located moth and is close; so moth chooses to play dead (deception)
7
Q
Predator avoidance: Fleeing
A
- Makes sense especially in open habitats
- Predators are often bigger, run faster
- Bigger animals may be able to run faster but smaller animals can zig-zag, jump, etc.
8
Q
Predator avoidance: Hide
A
- Relatively small size helps
- Camouflage or cryptic colouration
• Background matching
Disruptive colouration
• Transparency (common in aquatic systems)
9
Q
Predator avoidance: Stick Together
A
- If you can’t hide, then herd; especially in open areas
• Reduces individual chance of predation (dilution effect)
• Increases changes of predator detection
• Also conserves energy - Herd
• Can be multi species
• May serve to protect young
• Position is important: centre is safer
• But may also attract predators - Stick together
• Flood the market
• Seen in insects; r-selection – emphasize high growth rates, typically exploit less crowded niches, produce many offspring and few of them have probability of surviving to adulthood
10
Q
Predator avoidance: Call in your friends
A
- Mobbing calls; call in a mob
- Fairly common in birds
- Found in other animals like meerkats
- Why does this not increase individual predation risk by calling attention to prey?
• They do draw attention to the adults; but do it to protect young
11
Q
Predator avoidance: Fight
A
- Physically:
• Physical structures – ex: hedgehogs, porcupines, stingers on stinging slut moth, caterpillar, spikes on pufferfish
• Behaviour – ex: California ground squirrel kick sand in face of snake, or hagfish secrete slime; may be to protect nest or young - Chemically: produces secondary metabolites (organic compounds not directly involved in organism’s primary functions) that taste bad, cause illness or are fatal to predators
- which is better? Why? Cause illness because want to stop predator from trying to eat you
- Naïve blue jays feed on monarch butterflies; vomit; avoid monarchs; learning based on visual cues
- Make own toxin
• Fire salamander makes neurotoxic alkaloid in poison glands and excretes if caught - Get toxin from food
• Ex: monarchs eat milkweed, which contains cardiac glycosides
12
Q
Predator avoidance: Look Tough - Aposematism
A
- Aposematism warns of toxicity or bad taste (Monarch, granular poison frog)
13
Q
Limitations of aposematism
A
- Only works for predators with good colour vision UNLESS there’s also a pattern
- Prey must die for predator to learn
- Easy meals for predators that by-pass the defense (they are immune to it)
14
Q
When does aposematism work best?
A
- Toxin is emetic (causes vomiting)
- Predator is long-lived
- Prey occurs at relatively high densities
15
Q
Evolution of aposematism
A
- Apparently altruistic trait – which doesn’t seem to fit with our notion of evolution, natural selection, survival of the fittest…
- Once it is common it may be maintained by antiapostatic selection: selection in favour of the common form, against new, rare and or conspicuous forms BUT
- How can it increase population? Green beard affect (thought experiment)
- Selection for altruism to individuals who share a common, recognizable phenotype because this is generally caused by a common genotype
- Selfish gene wants only to propogate itself
- Altruism directed at other individuals who share that gene – requires specific markers for that altruistic behaviour to recognize the gene (a green beard or something else perceptible)
16
Q
Individual selection for aposematism
A
• Maybe conspicuous form will not be killed first after all
- Cryptic at distance, aposematic up close
- Combined with deimatic display (threatening/startling behaviour?)
- Avoidance of novel food by predator
- Maybe pattern has other benefits (thermoregulation, mating, territoriality)
- Maybe colouration comes with other warning cues such as smell
17
Q
Density dependence in aposematism
A
- Desert locusts; can be alone or in groups – have different pattern in colouration depending if they’re alone or group; can switch between colouration and patterns mediated by plant alkaloid as dietary switch occurs
- Aposematism may be more effective if you look like other unpalatable species (increased density-
Mullerian mimicry) - Common colours: red, orange, yellow and black
- Limits on Mullerian mimicry;
- Visual predators
- Some prey loss (though less due to multi-species participation)
