Midterm Review

Question 1

What are the components of the structure of ecological communities?

Answer 1

1) Species richness (S) = the number of species in a community.
2) Abundance (N) = the total number of individuals in a community (all species included) VS. Relative Abundance (P) = the percentage of individuals (ni) each species contributes to the total number of individuals (N) in a community.
3) Evenness = the spread of individuals among species.
4) Composition = the identity of species in a community.

Question 2

To be able to protect resources what do we need to do?

Answer 2

We must be able to understand HOW the ecosystem works: Understanding the processes that enable the maintenance of biodiversity. Biodiversity provides humans with services.

Question 3

What’s plotted on an accumulation curve?

Answer 3

Y axis = estimated species richness
X axis = number of samples

Question 4

What can accumulation curves be used for?

Answer 4

Accumulation curves can be used to estimate the total species richness in a community, and whether you have sampled enough or not.

Question 5

What does it mean if the accumulation curve plateaus?

Answer 5

it is an indication that you have sampled enough species in your study site

Question 6

What does it mean if your accumulation curve doesn’t reach a plateau and how can this be fixed?

Answer 6

It means your estimation of S (species Richness) is inaccurate and an increase in your sample size will fix this

Question 7

What is plotted on a rank abundance curve (AKA Whittaker plot)?

Answer 7

y axis = Relative abundance
x axis = Rank based on abundance

Question 8

What can rank abundance curves be used for?

Answer 8

Plotting relative abundance against rank is a common way to visually compare patterns of species richness and evenness between communities.

Question 9

What does the slope of the rank abundance curve tell you?

Answer 9

Flatter slope = more even

Question 10

What does an ordination graph show you?

Answer 10

This shows how similar these communities are in terms of species composition.

Question 11

In the ordination graph of the ant communities, what was the conclusion?

Answer 11

-There are obvious clusters, which draws the conclusion that species composition differ between ant communities with different foraging habitats.
-On average, there is less variation within a substrate type than between substrate types.

Question 12

What are the 3 approaches to map spatial patterns of community composition?

Answer 12

1) biomes = Large-scale regions describing spatial variations in plant growth form and climate
2) Ecoregions = Small-scale regions describing spatial variations in plant growth form and climate
3) Biogeographic Regions = Large-scale regions describing spatial variations in all species composition (animals, plats, fungi, etc.).

Question 13

Which of the 3 approaches to map spatial patterns of community composition is important for conservation?

Answer 13

Ecoregions

Question 14

Wallace’s zoogeographic regions VS Holt et al., what are the main differences?

Answer 14

Wallace: Was based on mammals’ global distributions. He divided the world into 6 biogeographic regions, each further divided into 4 subregions.
Holt et al.: Was based on terrestrial vertebrate distributions & phylogenetics.

Question 15

Between Holt and Wallace’s approach to zoogeographic regions, which was more accurate?

Answer 15

Holt

Question 16

Why are there more species in the tropics than in temperate regions? (4 hypotheses)

Answer 16

1) Evolutionary time: Tropical niche conservatism (Weins & Donoghue, 2004)
2) Historical Climatic stability
3) Productivity (currie & Paquin)
4) Heterogeneity

Question 17

Explain the Evolutionary time: Tropical niche conservatism (Weins & Donoghue, 2004) hypothesis

Answer 17

100 million years ago, the entire world used to be tropical. Most extant lineages had adapted to tropical conditions. Over time, the world started changing and continents started moving closer to the poles and the planet was getting cooler, giving rise to new temperate biomes. When these new biomes arose, there was tropical niche conservatism, making it hard for species to adapt to the temperate biomes.
For this reason, the tropics had a big head start on temperate biomes.

Question 18

Explain the Historical Climatic stability hypothesis?

Answer 18

In northern regions, there were multiple major episodes of freezing and warming. Along the equator, there was climatic stability over time; climate change velocity was lower in tropical regions than in temperate regions. Lower climate change velocity = reduction of extinctions & increase in survival of endemic species. Tropics are more stable due to the presence of mountains and valleys –– which trap hot and humid air, providing climatic stability. This promotes the preservation of endemic species.

Question 19

Explain the Productivity (Currie and Paquin) Hypothesis?

Answer 19

increase in evapotranspiration (proxy for energy) = increase in species richness

The tropics absorb a lot of energy, turning it into high net productivity -> a lot of primary producers -> supports a huge population of primary consumers -> supports a huge population of secondary consumers -> high species richness in the tropics.
Moreover, because we will have big populations, it is less likely that one population will go extinct (ecological drift is less likely to work).

Question 20

Explain the Heterogeneity Hypothesis?

Answer 20

Mountains create heterogeneity because you’re likely to have multiple types of biomes layered vertically over each other. And we will have a multitude of different species adapted to the different layers of that mountain = more richness

Question 21

Why do young mountains such as the Andes and Himalayas have higher species richness than older mountains?

Answer 21

Older mountains erode overtime = less vertically layered biomes

Question 22

What is succession?

Answer 22

gradual and (seemingly) directional change in community over time.

Question 23

Is succession deterministic or stochastic view?

Answer 23

It is a deterministic view of change of communities; it is very highly predictable.
There are still, however, stochastic aspects.

Question 24

What are the 6 characteristics of early successional or pioneer species (r-strategists)?

Answer 24

1) Small size
2) High growth rates
3) High degree of dispersal
4) High degree of per capita growth
5) Usually shade-intolerant
6) These species move in quickly, grow quickly but they can’t grow big (shade intolerant).

Question 25

What are the 4 characteristics of late successional or climax species (k-strategists)?

Answer 25

1) Larger size 2) Lower rates of dispersal and colonization 3) Slower per capita growth rate 4) These species grow to the point where they get bigger than pioneer species (shade tolerant).

Question 26

When does primary succession occur?

Answer 26

occurs on a site previously unoccupied by a community (on mineral soil; no organic matter present).

Question 27

What are some examples of primary succession?

Answer 27

can occur in areas with volcanoes, can occur following a glaciation episode (Pleistocene in North America).

Question 28

When does secondary succession occur?

Answer 28

occurs on previously occupied (vegetated) sites after a disturbance (organic matter still present).

Question 29

What are some examples of secondary succession?

Answer 29

can occur following a forest fire, can occur following a clear-cutting (e.g., Hubbard Brook Experimental Forest).

Question 30

What is a better term for succession?

Answer 30

Community assembly

Question 31

What is community assembly?

Answer 31

how communities are assembled over time from a regional species pool

Question 32

What is a species pool?

Answer 32

all the species that can disperse and establish themselves in a local community. BUT Not all species in your species pool can colonize your community.

Question 33

What 3 things determines the composition of species in a community?

Answer 33

1) dispersal = stochastic; makes it hard to predict who will colonize the area and when 2) Environmental filtering = deterministic; easy to predict who is adapted to conditions of the area just by knowing traits of species in species pool 3) Biotic interactions = deterministic; easy to predict which species will compete for which resources just by knowing the traits and similarities between the species in the area and in the pool

Question 34

What is Clements view on Community assembly?

Answer 34

Monoclimax Hypothesis (Clements): a very deterministic view of community assembly. According to Clements, the community is a highly integrated superorganism. To him, a community evolves the same way as a humans evolves (embryo to elderly). In this view, biotic and abiotic filters play a crucial role.

Question 35

What is Gleason's view on community assembly?

Answer 35

Gleason saw communities as an arbitrary concept and believes that each species responds independently to conditions. He doesn’t view them as a super-organism which makes it much harder to predict Individualist concept (stochastic assembly). Chance events played a crucial role.

Question 36

What are the 4 criteria for a metapopulation?

Answer 36

1) Habitat occurs in discrete patches. 2) Even large populations are at risk of extinction. 3) Habitat patches should not be isolated to allow recolonization. 4) Local population dynamics should not be synchronized.

Question 37

At the local or within-patch scale dynamics of metapopulations are based on what?

Answer 37

individual interactions; pop growth is governed by death/birth rates

Question 38

At the regional or metapopulation scale, dynamics are based on what?

Answer 38

Pop interactions; pop growth is governed by dispersal, colonization, and extinction/extirpation

Question 39

What is a source pop?

Answer 39

Patches with big populations tend to be overcrowded and they will send a lot of individuals out

Question 40

What is a sink pop?

Answer 40

Other populations are small (due to poor patch habitat for example), that they will act as a sink population –– receiving individuals from other patches.

Question 41

What is the rescue effect?

Answer 41

the increase in population size (and decrease in extinction risk) that occurs with an increasing rate of immigration.

Question 42

Why can't a lot of sink pops be rescued?

Answer 42

because they're so far away from source pops

Question 43

What is a solution to make sure smaller patches can be rescued by larger ones?

Answer 43

Ecologists have pushed the solution of corridors which are strips of suitable habitat that span between smaller patches and larger ones to promote rescue effect

Question 44

What happens to disconnected patches?

Answer 44

no rescue effect possible; species can go extinct by chance, leading to a decrease in species richness on that patch

Question 45

When is Species richness equilibrium (S) achieved in the theory of island biogeography?

Answer 45

When rate of immigration = rate of extinction

Question 46

What happens to immigration rates as the # of individuals on island increases in the theory of island biogeography?

Answer 46

immigration rates decline; fewer "new" species to colonize bc potential source pool = depleted.

Question 47

When is immigration rate 0 in the theory of island biogeography?

Answer 47

When all mainland species exist on the island

Question 48

What happens to the extinction rates on an island when there's an increase in species richness in the theory of island biogeography?

Answer 48

Extinction rates on the island will increase with increasing species richness since more species = more competition

Question 49

In the theory of island biogeography, how does the distance of an island from mainland and size of island affect S?

Answer 49

Distance: Far from mainland = lower S because less immigration Size: Small island = lower S just by chance that more animals will find larger islands (higher S)

Question 50

What are the 3 caveats of the theory of island biogeography?

Answer 50

1) Assumes all species are the same. Disregards differences in species autecology; in nature, some species may be better at dispersal, some may be more dominant competitors than others, etc. 2) It assumes that new arrivals affect the risk of competitive exclusion. Ignores the fact that mutualism exists in nature. 3) Biggest caveat: it ignores the role of speciation / diversification.

Question 51

What is Hutchinson's idea of an ecological Niche?

Answer 51

Hutchinson’s n-dimensional hypervolume: a species-defined space where it can survive, grow and reproduce in response to n-dimensional environmental factors. According to Hutchinson, species can coexist only if their niches have minimal overlapping in their niches. If they differ in their requirements, they will be able to coexist well.

Question 52

What are Niche dimensions in Hutchinson's idea of an ecological Niche?

Answer 52

Niche dimensions include resources (food, habitat) and conditions (temperature, humidity, pH).

Question 53

What is "n" in Hutchinson's idea of an ecological Niche?

Answer 53

“n” is an undefined value as it is hard to know how many factors need to be considered to define the niche of species.

Question 54

According to Hutchinson, when can species coexist?

Answer 54

Species can coexist only if their niches have minimal overlapping. If they differ in their requirements, they will be able to coexist well.

Question 55

What is a fundamental niche?

Answer 55

the full range of conditions and resources under which it can survive and reproduce.

Question 56

What is a realized niche?

Answer 56

the portion of the fundamental niche that the species actually exploits.

Question 57

What 2 factors cause a discrepancy between the realized and fundamental niche?

Answer 57

1) Competitive exclusion causing species to be compressed into their realized niche. 2) Dispersal limitations due to physical barriers (e.g., rivers, mountains, etc.)

Question 58

What is niche differentiation?

Answer 58

differences in the range and type of resources used, or in environmental tolerances.

Question 59

What is the idea of limiting similarity by hutchinson in regards to resource partitioning?

Answer 59

ecologically similar species coexist only if they have evolved sufficient differences in morphological traits to allow niche separation. Too much ecological similarity may lead to competitive exclusion.

Question 60

What is an example of an evolutionary effect that can explain why species can coexist?

Answer 60

Character displacement

Question 61

What is character displacement?

Answer 61

a shift in feeding niche that affects species’ morphology, behavior, and physiology

Question 62

Provide an example of character displacement:

Answer 62

If 2 closely related species are together in the same habitat and already have slight difference in the resources they exploit (e.g., seed size), natural selection will push these species to further diverge in food resource and then causing them to diverge further in morphological traits Over time, species A will start eating smaller seeds and species B will start eating bigger seeds -> both species will start evolving morphology appropriate to their respective seed sizes (refer to experiment with Darwin’s finches).