Unit 8 - Ecology

Question 1

What is the difference between density, population size, and dispersion in relation to a population?

Answer 1

Density = # of individuals per unit area/volume
Population size = # of individuals total
Dispersion = pattern of how those individuals are spread out or distributed

Question 2

What general mechanisms cause population sizes to increase or decrease?

Answer 2

Birth (reproductive rate) and immigration (influx of individuals from other areas) result in increase

Death (survivorship curve) and emigration (movement out) result in decrease

Question 3

Describe the three patterns of dispersion.

Answer 3

1. Clumped - individuals are grouped into patches

EX: May be associated with greater availability of food, mating behavior, favorable climate, or better defense against predation

2. Uniform - individuals are evenly spaced

EX: May be due to territoriality (defense of a bounded physical space against encroachment by other individuals)

3. Random - unpredictable spacing and the position of each individual is independent of others

EX: plants established by windblown seeds

Question 4

Describe the three survivorship curves.

Answer 4

Type I - flat and high at the start (low death rates during early/middle life) and then drops steeply (increasing death rates for older age classes). Applies to animals that produce few offspring but provide them with good parental care (EX: humans and other mammals)

Type III - drops sharply at the start (high death rates for the young) but flattens out eventually (declining death rates for those who survive the early period of die off). Applies to organisms that produce a lot of offspring but provide little to no parental care (EX: fish release millions of eggs)

Type II - intermediate linear graph; constant death rate over the organism’s life span (EX: invertebrates, lizards)

Question 5

What does a stair step survivorship curve mean?

Answer 5

Younger individuals have a higher survivorship than older individuals

Question 6

What is carrying capacity (K) and how does a population that reaches it respond?

Answer 6

Carrying capacity is the maximum population size a specific environment can sustain with the abundance of limiting resources it has.

In a population at its K, birth rate = death rate (zero growth)

Question 7

Exponential population growth model vs logistic population growth model

Answer 7

Exponential - J shaped curve, occurs in populations with abundant resources and lack of competition (ideal conditions)

Logistic - S shaped curve, occurs in populations who are approaching their carrying capacity, and thus zero growth rate, asymptote = K

Question 8

K selection vs r selection

Answer 8

K selection - density dependent selection; selects for traits that are favorable at high densities (near carrying capacity with lots of competition); exhibited by Type I organisms like humans

r selection - density independent selection; selects for traits that maximize reproductive success in low densities (uncrowded environments with little competition); exhibited by Type III organisms like hares

Question 9

What are density independent factors? Give one example.

Answer 9

These are factors that limit growth based on chance

EX: environmental disturbances like droughts or floods occur regardless of the size of the population, keeping it in check by wiping out a random portion of individuals

Question 10

What are density dependent factors? Give three examples.

Answer 10

These are factors that limit growth based on the density of the population. They either reduce birth rates or increase death rates [negative feedback]

EX 1: Limiting resources - increasing population density intensifies competition for nutrients and other resources which reduces reproductive rates

EX 2: Disease - as population density increases, the transmission rate of a disease also increases which increases the death rates

EX 3: Territoriality - available space for territories or nesting may be limited, thus controlling the population

Question 11

Community

Answer 11

A group of populations of different species living close enough to interact

Question 12

Name the three main types of interspecific interactions.

Answer 12

1. Competition (-/-)
2. Exploitation (+/-) – predation, herbivory, parasitism
3. Positive interactions or symbiosis (+/+) or (+/0) – mutualism, commensalism

Question 13

What is competitive exclusion and when does it occur?

Answer 13

Occurs when two species compete for the same resources. One of the species will use the resources more efficiently and have a reproductive advantage compared to the other, which will eventually lead to competitive exclusion.

This is the local elimination of the inferior competitor

Question 14

Ecological niche

Answer 14

The specific set of biotic/abiotic resources an organism uses in its environment; the role it has in its ecosystem

*two species cannot coexist permanently in a community if their niches are identical

Question 15

Resource partitioning

Answer 15

Differentiation of niches that enables similar species to coexist in a community (limits competition because they use different available resources)

Question 16

How might an ecologist test whether a species is occupying its complete fundamental niche or only a portion of it?

Answer 16

Observe whether the niche size changes after the addition of nutritional resources to the habitat

Question 17

Fundamental niche vs realized niche

Answer 17

Fundamental niche = niche potentially occupied by the species
Realized niche = the portion of the fundamental niche actually occupied by the species

Question 18

What is parasitism? Give an example.

Answer 18

A parasite derives its nourishment from another organism, its host, which is harmed in the process

EX: Ticks on dogs

Question 19

What is mutualism? Give an example.

Answer 19

Benefits both species in survival and reproduction

EX: animals that pollinate flowers or disperse seeds (bee-flower interaction)

Question 20

Species diversity vs species richness

Answer 20

Species diversity = variety of different kinds of organisms that make up the community (based on # of different species and the relative abundance of each one)

Species richness = # of different species

Question 21

What are invasive species? How do they harm the environment they are introduced to?

Answer 21

They are foreign organisms introduced to native species

They harm the environment by exploiting a new niche through outcompeting other organisms (capture more available resources → leave fewer for the native species → decreases their survival). They often grow rapidly due to a lack of predators or competitors in this new environment

Question 22

Food chain vs food web

Answer 22

Food chain = the transfer of food energy up one specific sequence of trophic levels (autotrophs/primary producers → herbivores/primary consumers → carnivores/secondary consumers → decomposers)

Food web = the linking of numerous food chains in a community

Question 23

Keystone species

Answer 23

Has a pivotal ecological role/niche in the ecosystem despite not being very abundant. If it is removed, the entire ecosystem will collapse

Question 24

What is ecological succession? Name two types of it.

Answer 24

After a severe disturbance (EX: volcanic eruption) that strips away all existing vegetation, the area is colonized by a variety of species. More species come and replace the original ones as the environment gradually recovers

Primary succession and secondary succession

Question 25

Describe the process of primary succession

Answer 25

Begins in a lifeless area with NO SOIL (EX: new volcanic island with only rock)

1. Only life forms initially present are prokaryotes/protists
2. Then the first macroscopic photosynthetic lichen + mosses colonize the area
3. Soil gradually develops as rocks weather and organic matter accumulate from the decomposed remains of early colonizers
4. Once soil is present, lichen + moss are replaced by grasses, shrubs, and trees
5. Eventually the area is colonized by plants that become the community’s dominant form of vegetation

Question 26

How is secondary succession different from primary succession?

Answer 26

Begins in an area with SOIL still intact (EX: forest after a fire)

Question 27

Ecosystem

Answer 27

The sum of all the organisms living in a given area and the abiotic factors with which they interact

Question 28

Energy flow vs chemical cycling

Answer 28

Energy flow - energy enters an ecosystem as sunlight and is converted to chemical energy by autotrophs, passed to heterotrophs in the organic compounds of food, and dissipated as heat.

Chemical cycling - chemical elements like carbon and nitrogen are cycled among abiotic/biotic components of the ecosystem

While chemicals are reused, energy enters, flows through, and exits out

Question 29

What is the role of detritivores/decomposers? Give examples of them.

Answer 29

Definition: They are consumers/heterotrophs that get their energy from detritus, which is nonliving organic material such as remains of dead organisms, feces, fallen leaves, and wood.

Function: They break down this organic matter from all trophic levels into inorganic compounds (chemical elements) usable by autotrophs/primary producers. When they excrete waste products or die, those compounds are returned to the soil for uptake by producers

EX: earthworms, prokaryotes, fungi

Question 30

What factors control primary production in terrestrial and aquatic (marine + freshwater) ecosystems?

Answer 30

Terrestrial - temperature and moisture (annual precipitation)

Aquatic - light and nutrients (nitrogen + phosphorous)

Question 31

How much energy is transferred between trophic levels? Where does the rest go? How does this benefit the ecosystem?

Answer 31

10%

the rest is dissipated as body heat

This limits the abundance of top level carnivores that an ecosystem can support

Question 32

Energy pyramid

Answer 32

Illustrates the net productions of different trophic levels in tiers and the loss of energy with each transfer [Joules]

Question 33

Water cycle (biological importance, forms available to life, reservoirs, key processes)

Answer 33

Biological importance - water is essential to all organisms and its availability influences the rates of ecosystem processes, especially primary production + decomposition in terrestrial ecosystems

Forms available to life - all organisms are capable of exchanging water directly with their environment

Reservoirs - oceans&raquo_space;> glaciers + polar ice caps > lakes, rivers, groundwater

Key processes - evaporation (transpiration) of liquid water by solar energy → condensation of water vapor into clouds → precipitation → surface/groundwater flow can return water to oceans

Question 34

Carbon cycle (biological importance, forms available to life, reservoirs, key processes)

Answer 34

Biological importance - carbon forms the framework of the organic molecules essential to all organisms

Forms available to life - autotrophs use CO2 during photosynthesis and convert the carbon to organic forms (C6H12O6) that are used by consumers

Reservoirs - fossil fuels, soils, the sediments of aquatic ecosystems, the oceans, plant/animal biomass, atmosphere

Key processes - photosynthesis by plants remove atmospheric CO2 while cellular respiration of producers/consumers and burning of soil fuels add it back. Consumers eat plants and break down plant molecules to obtain carbon and other atoms that they rearrange into new carbon-containing molecules.

Question 35

Nitrogen cycle (biological importance, forms available to life, reservoirs, key processes)

Answer 35

Biological importance - nitrogen is part of amino acids, proteins, and nucleic acids and is often a limiting plant nutrient

Forms available to life - plants can use NH4+ and NO3- [inorganic] and amino acids [organic]. Bacteria can use all those and NO2-. Animals can only use organic forms

Reservoirs - atmosphere (N2 gas)&raquo_space;> soils and sediments of lakes, rivers, oceans > surface water/ground water > biomass of living organisms

Key processes - nitrogen enters an ecosystem mainly thru nitrogen fixation (conversion of N2 to forms that can be used by plants to synthesize organic nitrogen compounds). The NH4+ released by consumers into the soil is converted by bacteria to NO3-, which is used by plants to make proteins and nucleic acids.

↓bacteria ↓
NH4+ → NO3- (nitrification)
NO3- → N2 (denitrification)

Question 36

Phosphorous cycle (biological importance, forms available to life, reservoirs, key processes)

Answer 36

Biological importance - phosphorous is a major constituent of nucleic acids, ATP

Forms available to life - inorganic phosphate (PO4 3-) which plants absorb and use in the synthesis of organic compounds

Reservoirs - sedimentary rocks&raquo_space;> soil > oceans > organisms

Key processes - weathering of rocks adds PO4 3- to soil slowly → spills into ground water/surface water → taken up by producers → incorporated into organic molecules and passed on to consumers → returned to soil/water by decomposition of biomass or excretion by consumers

Question 37

Describe two different strategies organisms use to

regulate body temperature and metabolism.

Answer 37

1. Endotherms use thermal energy generated by metabolism to maintain homeostasis and constant body temperatures.
2. Ectotherms lack efficient internal mechanisms for maintaining body temperature, though they may regulate their temperature behaviorally by moving
   into the sun or shade or by aggregating with other individuals.

Question 38

Describe two adaptations against predation

Answer 38

1. Cryptic coloration - prey is camouflaged by its coloring, making them hard to spot
2. Aposematic coloration - prey warns that it’s poisonous by being brightly colored

Question 39

What level of disturbance fosters the greatest species diversity and why?

Answer 39

Intermediate

If the level is too high, frequent and intense environmental stresses will wipe out many species that can’t tolerate them or that grow slowly

If the level is too low, competitively dominant species will be able to exclude less competitive ones. The community will rely on interspecific interactions

Question 40

Primary production

Answer 40

The amount of light energy converted to chemical energy (in the form of organic compounds) by autotrophs

The amount of all photosynthetic production sets the spending limit for the energy budget of the entire ecosystem

Question 41

Gross primary production (GPP) vs net primary production (NPP)

Answer 41

GPP = total primary production in an ecosystem
NPP = amount of energy available to consumers 
(NPP = GPP - Ra)

Ra = the energy used by primary producers for autotrophic respiration

Question 42

How does species diversity affect the population’s resistance to change?

Answer 42

Higher genetic diversity = more individuals that can withstand different selective pressures = higher resistance to environmental disturbances = lower survival of invasive species

Question 43

Why cannot energy be cycled through an ecosystem?

Answer 43

Second law of thermodynamics - in any energy transfer, some of the usable energy is lost as heat, so the entropy of the universe is always increasing