Predation and Herbivory I

Question 1

an example of exploitation

Answer 1

an antelope (species 1) killed and consumed by a lion (species 2)

Question 2

What does Optimal foraging theory say that dietary specialization depends on:

Answer 2

• encounter rate: time it takes to search and find prey
• handling time: time it takes to subdue/consume/ digest prey

Question 3

Why do Herbivores tend to be Specialists?

Answer 3

• specializing on specific plant parts and/or species
• most herbivores eat leaves
• ultimately leads to reduce survival, growth and/or reproduction of plants

Question 4

What is a Grazer?

Answer 4

• type of herbivore
• feed on (nutrient rich) low-growing, non-woody plants e.g., grasses, herbs
• ex. horses, cattle, sheep

Question 5

What is a Browser?

Answer 5

• type of herbivore
• feed on (nutrient poor) high-growing biomass, e.g., leaves, twigs
• ex. moose, giraffe, goats

Question 6

Ecological Impact of Herbivore?

Answer 6

• herbivore has a little bit of nuance to it
• rarely immediately kills the eaten plant
• plants usually recover, albeit their growth/reproduction
  -herbivory might stimulate growth in grass

Question 7

Exclosure Experiments

Answer 7

a method to study the effects of herbivory/predation on a species/community
- e.g., by using fences, mesh or inaccessible position

Question 8

The effect of grazing geese on grass growth (Jefferies)

Answer 8

• created 5mX5m exclosures to keep geese out
• compared to plant growth in the presence and absence of goose grazing
• had both temporarily and permanent exclosures to measure long and short terms effects
• above-ground biomass decreased, but primary productivity increased

Question 9

How does Grazing increase Production?

Answer 9

productivity is elevated only when:
- light grazing: removal of dead plant material
- feces acting as fertilizer/source of nutrients
- grazing occurs in early summer- plants still have time to grow and recover

Question 10

What makes carnivores generalists?

Answer 10

they eat prey in relation to their availability without showing a preference for any particular prey

Question 11

An exception to carnivores being generalists

Answer 11

lynx and coyotes eat more hares than would be expected even at low abundance

Question 12

prey switching

Answer 12

when predators concentrate on whatever prey is most abundant

Question 13

example adaptations for catching prey:

Answer 13

• body form of cheetahs are specialized for bursts of speed
• snake skull bones are not rigidly attached
• venom
• mimicry
• the ability to detoxify poisons

Question 14

How do Predators impact Prey Populations

Answer 14

• food availability
• consumptive effects of predators
• non-consumptive effects of predators

Question 15

The Lynx and the Hare

Answer 15

• most famous example in ecology on predator-prey dynamics
• population cycles of these two species are very well documented because HBC kept trapping records for approx 200 years
• data show that populations peak about every 10 years
• hare populations rise and fall in synchrony across broad regions throughout Canada
• modelling suggests that the lynx fluctuations depend on the hare, but hare populations are affected by lynx and other factors

Question 16

Consumptive effects of predation

Answer 16

direct effects of predators on prey populations through the capture and consumption of living prey

Question 17

non-consumptive effects of predation

Answer 17

• changes to prey that are due to predators being present, including shifts in morphological traits, stress physiology and altered behavior
• can only result in reductions in reproduction when the direct consumptive effects of predation are high

Question 18

The Lynx and The Hare

Answer 18

1. as plant food availability increases, the hare population increases
2. hare population start to decrease as food is depleted
3. this decline is further accelerated by predation
4. as the hare population decreases beyond a threshold, predator populations themselves start to decline
5. after several years, vegetation start to recover and increase
6. in turn, this leads to an increase in hare populations and the cycle begins again

Question 19

describing population growth of prey (lotka-volterra model)

Answer 19

the change in the number of prey over a period of time = the per capita growth of the prey (rh) multiplied by its population size (Nh)

Question 20

What is “capture efficiency”?

Answer 20

the proportion of encounters between predators and prey that results in the predator capturing/eating the prey
- aka the success rate of the predator

Question 21

What is the “conversion factor”?

Answer 21

how many prey are required to “produce” one predator
- ex. how many prey individuals a female needs to consume to make one offspring