Food Webs and Symbiosis

Question 1

Trophic Cascade

Answer 1

Occurs when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next trophic level from predation

Question 2

Bottom-Up control

Answer 2

Nutrient availability, drives primary productivity - drives densities of high trophic levels; increase in primary productivity = increase in trophic levels above the bottom up cascade

Question 3

Top-Down Control

Answer 3

Predators control densities of lower trophic levels

Question 4

Keystone Species

Answer 4

one whose impact on its community of ecosystem is disproportionately large relative to its abundance

Question 5

2 example of keystone species from different habitats.

Answer 5

• Starfish are keystone species in intertidal habitats

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Question 6

Stability of food webs?

Answer 6

Connectivity (level of connectedness between species within a system); greater connections = more stable food webs tend to be

Question 7

Define Symbioses

Answer 7

living together of 2 heterospecific organisms (either reciprocal or unilateral dependency)

Question 8

Phoresis:

Answer 8

2 species interactions, non-obligatory relation, no fitness advantage/detriment for either participant (ie. barnacles and mussles)

Question 9

Mutualism

Answer 9

Reciprocal benefit for both participants, evolution of cooperation for mutual benefit, both species exhibit high fitness in the presence of each other (ie. anemone - zooxanthellae)

Question 10

Commensalism

Answer 10

Asymmetrical benefit, fitness increase for one participant, no fitness consequence for the other participant (ie. remora - fish/shark)

Question 11

Parasitism

Answer 11

Asymmetrical benefit, one species gains a fitness advantage while other species incurs some degree of harm and loss of fitness (ie. trematodes/snails)

Question 12

Parasite influence on food web stability or instability of a system.

Answer 12

Make up over 50% of organisms and occur in pretty much every phyla; increase in parasite = drive stability; especially when increase in marine food webs with parasite species but transmission via predation.