Lecture 11

Question 1

Give the formal definition of +- interaction (one benefits and the other is harmed)

Answer 1

Species in a higher trophic level consuming or partly consuming organisms in a lower trophic level

Question 2

Give some basic types in +- interactions

Answer 2

. True predators
. Parasites
. Parasitoids

Question 3

What are true predators?

Answer 3

Consumes/ kills other species

Question 4

Describe parasites

Answer 4

. Have to associate with a host
. Often close obligate association with host
. Rarely kill host

Question 5

Describe parasitoids

Answer 5

. Parasites that lay their eggs into a host
. Mainly Hymenoptera (wasps), some Diptera (flies)
. Host killed- will eat the host from the inside.
Host can be egg, larval, pupal, adult stage
. Hyperparasitoids- parasitoid the larvae of the parasitoid

Question 6

Describe infectious disease

Answer 6

. Typically caused by bacteria, viruses or fungi. Plants particularly vulnerable to fungal infection (to infectious disease)
. Immune response of hosts
. Susceptible, exposed, infectious, resistant (SEIR) models used to predict spread
. Vectors (especially invertebrates) used to spread some diseases
. Coevolution of host and disease organism over time

Question 7

Explain the infectious disease Myxoma virus and what happened

Answer 7

. Those that have been exposed several times have a lower mortality rate
. Myxoma virus originates from South America where it has little effect on native rabbit (co-evolution between lethality and rabbit resistance)
. European rabbits severely affected
. Introduced to UK in early 1950’s and within 2 years 95% were dead
. Virus lethality declines
. Rabbit populations now recovered

Question 8

What are the types of defence strategies that plants have against herbivores?

Answer 8

Chemical
Mechanical
Nutritional
Tolerance

Question 9

How does the chemical defence that plants have against herbivores work?

Answer 9

Producing chemicals that are noxious or poisonous to herbivores

Question 10

What are the mechanical defences that plants have against herbivores?

Answer 10

Developing structures like thorns that make it harder for animals to eat them

Question 11

What are the nutritional defences that plants have developed against herbivores?

Answer 11

Growing structures that are less nutritious for grazers (have less N and P) (so, don’t waste nutrients e.g. grass)

Question 12

What are the tolerance defences that plants have developed against herbivores?

Answer 12

Adaptions to regrow quickly after being grazed

Question 13

What are the indirect effects of plant defences?

Answer 13

. Thistles and nettles put resources into spines and stings
. Defend from vertebrate herbivores
. Relatively high insect herbivore species richness and population
. Tend to be fewer chemical defences so more insect eat them

Question 14

What are monophagous predators?

Answer 14

Single prey (predators that only eat a certain species of prey)

Question 15

What are oligophagous predators?

Answer 15

Predators that only eat a few types of prey

Question 16

What are polyphagous predators?

Answer 16

Predators that eat many prey species

Question 17

Which of the type of predators (monophagous, oligophagous or polyphagous- predators vary in food specialisation) are more likely to have couples oscillations to prey?

Answer 17

Monophagous predators

Question 18

How do predators select their prey? Give an example

Answer 18

Predators choose the most profitable prey.
An example is pied wagtails and flies, middle sized flies are most common to go for, because if the wagtails went for larger fly then it would use more energy to deal with the prey because they only have small beaks

Question 19

Explain what coevolution is and how it works

Answer 19

. Predators evolve to catch their prey, but prey evolve to avoid predation
. Speed, defence mechanisms, poisons etc.
. Predator cannot ‘coevolve’ in several different directions simultaneously
. Pressure for specialisation
. But most avoid over-reliance on an unreliable prey
. If prey has evolved strong defence mechanisms- tendency for specialised predators

Question 20

A longer handling time (predation) compared to a short search time and what kind of predators are they? Give an example of a predator like this

Answer 20

Search time short compare to handling time
These predators are specialists
E.g. lions are specialists on prey that can be pursued profitably

Question 21

A shorter handling time (predation) compared to a long search time and what kind of predators are they?

Answer 21

Search time long compared to handling time

These predators are generalists

Question 22

Explain predator switching with an example

Answer 22

Polyphagous predators select prey
E.g. predatory water bugs Notonecta feeding on either isopod ((Asellus) or mayfly larvae (Cloeon)- predation efficiency on Asellus also improved with exposure (become more efficient at catching the prey when frequency increases) (fluctuates in what they predate on, not consistent)

Question 23

Explain how predation is linked to intraspecific competition

Answer 23

. Increased population leads to less intraspecific competition among prey because predators are thinning them out
. Predation stabilising relative to intraspecific competition
. But complicated by predator selectivity (e.g. old, weak selected) select certain individuals and this can destabilise population dynamics

Question 24

Explain how parasites work/ what affects they have on the host, hosts defences and which species are the most hosts in?

Answer 24

. Reduces host growth rate, survival reproduction
. Energy diverted to parasite
. Destabilising effects on population dynamics- less regular, more chaotic
. Inverse density dependence
. Host behaviours may change due to parasite
. Host defences (and parasite counter-defences) but both have costs
. Most host species can have more than one species of parasite, but is highest when host is bird, mammal or plant (can have lots of parasites)

Question 25

Give an example of a parasite that impacts the behaviour of a host to facilitate its own spread

Answer 25

Yellow dungfly and fungus:
Flies infected by the fungus perch in an atypical position, from which fungal spores can easily spread to healthy flies.
Healthy flies typically perch on the upper surfaces of low-lying vegetation- where they are exposed to fungal spores

Question 26

What are the ecological impacts of parasites and diseases? Give examples

Answer 26

. May cause near extinctions of host
. Greatly reduce distribution ranges
. Affect host population dynamics
. Wider landscape structure might be affected
. E.g. Asian Cryphonectria fungus on American chestnut tree (almost all gone now)
. E.g. trematode worm parasites on Atlantic Corophium hosts amphipods (live in the soil-are filter feeders and gets these parasitic worms)

Question 27

Explain the affects that seed/plant herbivores have an plants and how plants react

Answer 27

. Seed herbivores- direct impact on next population generation of plants
. Grazers- less likely to kill plant; complex, vegetation community dynamics
. Dicotyledenous plants and non-graminoid monocots: physical and chemical defenses
. Grasses: regrowth at soil level
. Moderate levels of grazing can alter vegetation structure or soil chemistry, sometimes benefiting NPP (Net Primary Productivity), but excess grazing is damaging
(Medium grazing is the best)