L20 - Competition and predation Flashcards
How did Charles Darwin define competition in 1859?
It is the struggle for existence where individuals with advantageous variations have a better chance of survival, leading to natural selection
Where does most competition occur?
Most competition happens within a species, but there is also competition between species
How is competition linked to population numbers?
Competition is closely tied to population size and can be studied using mathematical models similar to those for population growth
What does the logistic growth equation for two species account for?
It incorporates the effects of one species on the growth rate of the other.
What is the Lotka-Volterra model used for?
It modifies logistic equations to include the competitive effects of species on each other using parameters
𝛼 and 𝛽
What are the possible outcomes of competition between two species?
- Species 2 eliminates Species 1.
- Species 1 eliminates Species 2.
- Either species eliminates the other depending on initial population sizes.
- Both species coexist if conditions allow
What does the competitive exclusion principle state?
Two species cannot coexist if they occupy very similar niches
How does resource separation (d/w ratio) influence species coexistence?
d/w<1: Species cannot coexist.
1<d/w<3: Some competition occurs.
d/w>3: Species coexist harmoniously.
What is character displacement, and how does it help species coexist?
It’s the adaptation of species to exploit non-overlapping niches, often driven by morphology differences.
How do prey populations grow without and with predators?
Without predators:
dN/dt=rN.
With predators:
dN/dt=rN−sPN, where
sPN represents prey removal by predators.
How do predator populations grow?
With prey:
dP/dt=esPN−mP, where
esPN is predator growth rate and
mP is predator death
What are some defenses employed by prey against predators?
Chemical defenses with aposematic coloration: Bombardier beetles, ladybirds.
Cryptic coloration: Grasshoppers, seahorses.
Batesian mimicry: Hoverflies mimicking wasps.
Müllerian mimicry: - - Similar warning signals across species, e.g., butterflies.
- Physical defenses: Turtle shells, beetle exoskeletons.
- Intimidation displays: Frilled lizards, porcupine fish.
- Predator satiation: Cicadas emerging in large numbers
What are the possible functions of zebra stripes?
Apparent size increase.
Visibility in poor light.
Dazzling predators with moving patterns.
Camouflage in tall grass.
Social benefits for individual recognition.
Fitness indication through stripe irregularities.
Thermoregulation via heat absorption.
Protection from biting flies like tsetse flies.
How do zebra stripes reduce attraction to horseflies?
The stripes reflect polarized light in a way that disrupts the attraction of horseflies, reducing their prevalence on zebras
What factors make extinction more likely?
Features such as specialized niches, low population sizes, and environmental changes increase extinction risk
