Species Interactions and Community Structure

Question 1

Keystone species

Answer 1

a species when removed will have a significant change in community structure;
impact on the community is disproportional to its biomass;
reduce likelihood of competitive exclusion [predatory activity] which increases the number of species that could coexist in community

Question 2

Wetland Reeds Food webs

Answer 2

Wetland reeds were attacked by herbacious flies [GIRAUDIELLA INCLUSA] which in turn were preyed upon by 14 parasitoid wasps

Weak and Strong feeding interactions means that removal of certain species [e.g. BLUE TIT] would affect to different degrees certain parasitoid wasps, herbivores, and plants

Question 3

Relationship between # of species, # of predators, and diversity

Answer 3

Paine found that an
INCREASE IN # OF SPECIES would
INCREASE PREDATOR PROPORTION in turn INCREASING DIVERSITY
–> greater predatory pressure
–> manages and reduces dominance of species
> One starfish specie removal saw a decline of 15 to 8 species

Question 4

Consumers’ Effect on Local Diversity;
HOW DOES PREFERENCE OF A SPECIES AFFECT COMMUNITY STRUCTURE?

Answer 4

Influence of intertidal snail [LITTORINA LITTOREA] on algal community: green [ENTEROMORPHA SPP.] and red [CHONDRUS CRISPUS]

> Enteromorpha&raquo_space;> Chondrus Crispus so WITHOUT Littorina littorea, crisupus is competitively displaced
Littorina littorea is preyed upon by carcinus maenus

Low snail density: Enteromorpha dominates
Medium snail density: competitive exclusion eliminated, algal diversity increased
High snail density: Snail feeding requirements mean that BOTH preferred & unpreferred consumed, algal diversity decreased

Question 5

Fish as a Keystone Species

Answer 5

California Roach and Steelhead Trout act as important predators of flies and frys to maintain algal diversity

Question 6

KEYSTONE SPECIES VS DOMINANT SPECIES GRAPH

Answer 6

Y-axis: Impact of Species
X-axis: Relative biomass of species

High impact, low biomass = KEYSTONE
High impact, high biomass = DOMINANT

Question 7

Seed Dispersal Mutualists as Keystone Species

Answer 7

Seed-dispersing ants bury seeds in sites safe from PREDATORS and FIRES

> Invasive Argentine Ant species displace many native ant species –> substantial reductions in seedling recruitment by plants producing LARGE seeds

Question 8

Cleaner Wrasse

Answer 8

LABROIDES
removes parasites and dead tissues

Question 9

Indirect Interactions

Answer 9

effects on one species on another through a third species

1. TROPHIC CASCADE
2. INDIRECT COMMENSALISM
3. APPARENT COMPETITION

Question 10

Indirect Commensalism: BEAVERS

Answer 10

One species is INDIRECTLY benefited from another species while it is neither helped nor harmed

> Beaver tree-cutting activity provided stump sprouts –> Beetles prefer consuming high nutrient stump sprouts –> Beetles grow larger faster and utilize defensive compounds found in leaves

Question 11

Apparent Competition: BRASSICA NIGRA

Answer 11

Negative effects between two competitors who share a common predator or herbivore
–> One species may facilitate the presence or increase the abundance of the predator which suppresses the second species

> Plant BRASSICA NIGRA shelters mammals which increase herbivory of NASSELLA PULCHRA

WITH BRASSICA NIGRA: gradient of decreasing NASSELLA PULCHRA density is formed from increase in herbivory
WITHOUT BRASSICA NIGRA: uniform density of NASSELLA PULCHRA