Lecture 27

Question 1

How are community interactions classified?

Answer 1

they are classified according to whether they help (+), harm (-), or have no effect (0) on the species involved

+/+ mutualism

-/- competition for resource

+/- predation

+/0 commensalism

Question 2

what is commensalism?

Answer 2

the interaction in which one species benefits and the other is neither harmed nor benefited.

Question 3

Host-parasite interactions +/-

Answer 3

• parasites are predators that eat prey in units of less than one
• tolerable parasites are those that have evolved to ensure their own survival & reproduction but at the same time w minimum pain & cost to the host

Question 4

What are some features of parasites?

Answer 4

• smaller than host
• live on / in host for extended time
• usually don’t kill host
• host may recover from parasite
• the habitats of parasites are themselves alive

Question 5

What are some of the features of the hosts of parasites?

Answer 5

• grow
• respond
• evolve
• move

Question 6

Examples of parasites

Answer 6

protozoans
animals
fungi
plants

(half of arthropods are parasites)

Question 7

What are keystone predators?

Answer 7

• helps to define the community
• if it is removed, the community will be drastically different or cease to exist

seastars imp cause they eat some mussels

Question 8

Nutrition from leaves – choose:

Answer 8

• higher available nitrogen
• lower levels of toxic chemicals

Question 9

Example of indirect effects of predation

Answer 9

• e.g. hiding (from spiders e.g. leads to less feedings = population declines)

impact is as strong as direct predation

can also affect SPATIAL ARRANGEMENTS e.g. birds will nest far away from area of predators

Question 10

What are the effect of grazing?

Answer 10

• change composition and structure
• increase cover
• increase exotic weeds
• decrease plant species richness

Question 11

Define predation.

Answer 11

predation is a widespread exploitative inter-species interaction that has profound effects on the structure and functioning of ecological communities

Question 12

What is the topological food web?

Answer 12

focus on number and distribution of connections, using data

Question 13

What are trophic cascades?

Answer 13

predator-prey effects that alter the abundance, biomass or productivity of a species, functional group or trophic level across more than one link in a food web

e.g. big fish eat little fish, little fish normally eat algae, so now algae increases

Question 14

Distinguish between top-down and bottom-up control.

Answer 14

top-down control: when predators have an effect on communities

bottom-up control: when producers have an effect on predators