Predation

Question 1

Are the majority of species autotrophs or heterotrophs?

Answer 1

heterotrophs

Question 2

What are the differences between generalists and specialists?

Answer 2

Generalists:
- Polyphagous = feed on wide range of foods
- Show clear preferences but can eat many different things
- = most carnivores

Specialists:
- Monophagous = eats only one kind of food OR oligophagous = eat only a few species, usually related
- focus on eating parts of an organism
- = parasites and insect herbivores

Question 3

What are the advantages do generalists have?

Answer 3

+ easy to find food
+ no seasonal constraint

Question 4

What are the advantages of being a specialist?

Answer 4

+ highly efficient at feeding
+ Monopolise resources = keep exclusively for themselves

Question 5

What are examples of plant defences and what do they aim to do?

Answer 5

These strategies aim to not kill or harm herbivores but make if inefficient for generalists to feed on them so they don’t bother trying e.g.
- most biomass = Indigestable compounds and remainder is filled with toxins or enzyme inhibitors to slow digestion
- mechanical barriers- tough tissues, spines, hairs

Question 6

Why does overcoming plant defences put specialised species at an advantage + example?

Answer 6

Species who are the only ones tolerant to a certain plant avoid any interspecific competition for food
e.g. Vomit fruit = toxic to fruit flies as fatal for them to land on
- exception = Drosophila sechellia- tolerates toxin avoiding interspecific competition

Question 7

What is another obstacle faced by plant consumers?

Answer 7

Their tissues contain a very different balance of nutrients- dominated by carbohydrates and indigestable chemicals and only small proportion of protein, fat + minerals
- animal tissue requires mostly protein with the remainder being fats and minerals

Question 8

What is the greatest challenge for herbivores?

Answer 8

Need to maximise nitrogen intake:
- to be 50% efficient they need to eat 20 x body weight to manufacture sufficient protein
- But most nitrogen is locked up in complex molecules and unavailable to consumers- so 50% = overestimate

Question 9

What is a solution to herbivores greatest challenge?

Answer 9

Eat meat as this contains the right balance of nutrients for their diet

Question 10

What are the challenges to eating meat?

Answer 10

Prey evolve defences
Catching prey is costly to acquire and sometimes dangerous
Once eaten and digested the energy transfer from one trophic level to the next is inefficient

Question 11

What are the 2 general categories of predators?

Answer 11

Predators that actively hunt
Predators that sit and wait e.g. web-building spiders

Question 12

What are the 2 general categories of predators?

Answer 12

Predators that actively hunt
Predators that sit and wait e.g. web-building spiders

Question 13

What are the 5 stages of predatory behaviour?

Answer 13

1. Detection
2. Pursuit
3. Catching
4. Handling
5. Consumption

Question 14

How does density of populations affect predation?

Answer 14

3 functional responses:

Type I = density of prey increases linearly until predators are satisfied and number of prey consumed levels off at a maximum rate

Type II = prey density increases until increased handling time so consumption slows

Type III = Lower rates of predation when prey are rare but speeds up when prey more abundant

Question 15

what is an example of a type I feeder?

Answer 15

Filter feeders e.g. basking sharks- density of plankton increases beyond consumption = proportional mortality drops

Question 16

What is an example of a type II feeder?

Answer 16

Pelican- struggles to store more fish in mouth as abundance increases- so increased density will result in predation rates slowing once maximum is reached

Question 17

What are the causes of type III reponses?

Answer 17

• prey might hide in refuges = inaccessible until hiding place fills up
• Generalist predators are able to switch prey when one becomes less abundant
• Predators lack handling experience with rarer prey or form a search image for potential rare prey

Question 18

What is an example of a type III predator?

Answer 18

Predatory backswimmer- feeds on mayfly larvae and isopods
- at lower densities mayfly larvae are predated on less relative to isopods and vice versa when they are more common

Question 19

Name and define a type of animal defence?

Answer 19

Aposematism = warning colouration
- herbivores store poisons obtained from diet, usually from toxic plants

Question 20

Describe an example of aposematism

Answer 20

Cinnabar moth feeds on ragwort plants = poisonous enough to kill horses
- cinnabar moth tolerates toxins and stores them as a caterpillar and retains them as a non-feeding adult
= results in both having bright contrasting colours which advertises to predators to avoid them

Question 21

Name and define 2 other types of animal defences.

Answer 21

Crypsis = camouflage- not only visual but can be chemical

Mimicry = appears to be another species considered to be harmful- doesnt need to be perfect but enough to deter predators so they can escape

Question 22

What are the 2 types of mimics and how are they different?

Answer 22

Batesian mimics = edible species that imitate one that is toxic or dangerous
Mullerian mimics = harmful species that mimic other harmful similar species so predators learn one common signal to know to avoid them all

Question 23

What is an example of a behavioural defence and what is the disadvantage?

Answer 23

e.g. Tadpoles can detect dragonfly larvae via chemicals in water and reduce their activity
- High cost as time spent hiding reduces foraging time = loss of fitness

Question 24

What is one common disadvantage to all defences?

Answer 24

They are costly so are only worth maintaining if effective at deterring predators

Question 25

Why is the world green?

Answer 25

Plants are difficult to eat due to their defences and little protein they contain

Predators control populations of herbivores
- presence of just herbivores = barren environment
- absence of herbivores = green environment

mesopredators are controlled by top predators which results in less predation of herbivores so more barren environment

Question 26

What are mesopredators?

Answer 26

middle-ranking predators

Question 27

Give an example of how prey drive predator populations.

Answer 27

Canadian Arctic- Hudson Bay fur company kept records over many decades of the number of pelts of snowshoe hares and lynx that were traded
- populations of lynx follow and are closely determined by hares

Question 28

Give an example of predators driving prey populations

Answer 28

Parasitoids live inside bodies of other organisms, consuming tissue and eventually killing them
e.g. California scale insect = sap-feeding pest
outbreak = parasitoid lay its eggs under hard shells of insects
prey populations boom and so do parasitoids which suppress scale of insect populations to same level as trees with no outbreak

Question 29

How does predation alter the outcome of competition among prey (example)?

Answer 29

Spadefoot toad = highly active swimmer so is able to feed and grow faster than spring peeper
- absence of predators = spadefoot wins in competiton and spring peppers are almost excluded
- Predatory newts present = newts feed on spadefoots and spring peepers have higher rates of survival

Question 30

Is energy lost or gained at each trophic transfer?

Answer 30

Lost

Question 31

How much energy is transferred between each trophic level?

Answer 31

1-25%

Question 32

Is energy more efficient on land than water and why?

Answer 32

More in water due to buoyancy of water reducing energy required for predator to move + most species are poikilothermic and therefore expend less metabolic energy overall

large proportion of plant material is locked in indigestable structural tissues + defences
- which a lot of is inedible or inaccessible and therefore decays when plant dies

= Plants grow larger and live longer than their herbivores = builds up lots of biomass- so biomass is concentrated in the bottom of biomass pyramid
- this is opposed to an aquatic ecosystem which is the opposite

Question 33

Define: Poikilothermic

Answer 33

Cold-blooded

Question 34

How do marine systems have inverted biomass pyramids?

Answer 34

1. algal tissue (=primary producer) is easy to digest so turnover is quick
2. Algae then consumed by larger herbivores which are then consumed by larger predators that live longer- so most living tissue is held in larger predators which control accumulation of material in levels below them

Question 35

are natural systems controlled more by bottom-up processes deriving from primary producers or by top-down control from predators?

Answer 35

Both but depends on which trophic level is considered:
- plants on their own will compete strongly with one another, but once herbivores are present = regulation switches to predation as herbivores compete for plants to eat

+ carnivore successive layers = dominant process regulating each layer switches from top-down to bottom-up