Chapter 3

Question 1

ecological succession

Answer 1

Ecological succession is the gradual replacement of one assemblage of species by another as conditions change over time

Question 2

two basic types of succession

Answer 2

• Primary succession

- Secondary succession

Question 3

primary succession

Answer 3

Primary succession is the colonization of a previously unvegetated surface, where little or no soil exists
e.g., when a glacier retreats or a landslide removes all traces of the vegetation of the previous ecosystem
The next stage in successional advance is usually invasion by herbaceous plants such as grasses and ‘weed’ species
The seeds that lie ‘in wait’ in the soil are considered to be part of the soil seed bank
The next stage is hardy shrubs and light tolerant trees, with trees dominating the final stage
Each stage along the way is known as a seral stage

Question 4

primary colonizers

Answer 4

Primary colonizers are the first species to occupy the area, and must be able to withstand harsh conditions
e.g., lichens (and later, mosses) (grasses in dune systems)

Question 5

climax community

Answer 5

The last stage of succession
A relatively stable, long-lasting, complex, and interrelated community of organisms
Influenced by climate (climate climax) and can be determined by soil factors (edapic climax)
In the first half of the twentieth century, it was believed that vegetation would reach a well-defined, stable stage called the climax community (final stage of succession).This stage was believed to be in equilibrium with the environment
In the second part of the twentieth century it became clear that equilibrium conditions are rare
Disturbances are so common that most systems never reach a stable climax stage
fires, insect infestations, flooding, ice storms

Question 6

disturbance

Answer 6

Process that alters ecosystem structure and function
Mountain Pine Beetle invasion in Western Canada
Many disturbances are natural and integral parts of healthy ecosystem functioning
Recovery patterns following disturbance depend on many factors
Ecosystems and landscapes are dynamic, interacting in complex ways, often unpredictably, and over large spatial and time scales.

Question 7

cyclic succession

Answer 7

Succession is not always linear.
e.g., hardy shrubs and trees can be first colonizers
Cyclic succession may occur when a community has progressed through several seral stage but is then returned to earlier stage by disturbance
Seral stages may blend into each other rather than being discrete
These blended areas have high species diversity and are known as ecotones; richer zones between communities

Question 8

mature community

Answer 8

Communities do not always reach a stable climax community, however the species assemblage that is more constant over time is characteristic of a mature community.
‘Climax’ vegetation is strongly influenced by climate (climax climate)
Soil can be more important than climate in determining community composition (edaphic climaxes)

Question 9

secondary succession

Answer 9

Secondary succession is the sequential development of biotic communities on previously vegetated surfaces that have soil cover, and that have been disturbed, e.g., abandoned farm fields
Faster than primary succession, and initiated by invading species such as annual ‘weeds’
Similar processes also occur in aquatic environments; the natural aging process is called eutrophication
–Can be a challenge for farmers and resource managers

Question 10

as succession occurs..

Answer 10

• NPP declines

- biodiversity increases

Question 11

intermediate diversity hypothesis

Answer 11

suggests that diversity will not increase indefinitely; and that moderately disturbed ecosystems have higher biodiversity than those that experience either high or low disturbance

Question 12

intermediate disturbance hypothesis

Answer 12

A hypothesis suggesting that ecosystems subject to moderate disturbance maintain higher level of diversity compared to low or high levels of disturbances

Question 13

effects of human activities

Answer 13

Humans influence ecological succession
We often keep ecosystems in an early stage
Agriculture, forestry
Increased productivity
Faster nutrient and water cycling, with greater losses
Reduced biodiversity, especially at higher trophic levels
Increase in pioneer species

Question 14

changing ecosystems

Answer 14

In the early 1970s, lakes in the Okanagan (BC) were invaded by Eurasian Water Milfoil, which later spread to many other lakes in southern BC and other provinces

Question 15

inertia

Answer 15

is the ability of an ecosystem to withstand change, while resilience refers to the ability to recover to the original state following disturbance

Question 16

invasive alien species

Answer 16

Organisms found in an area outside their normal range are considered alien species
e.g., Purple Loosestrife and Eurasian Water Milfoil
Species that multiply quickly, out-compete native species, and change native habitats are considered to be invasive alien species
Invasive alien species are often fast-growing generalists that can alter growth form, reproduce quickly both sexually and asexually, disperse readily, and associate with humans

Question 17

invasive species

Answer 17

Invasive species are second only to habitat destruction as a leading cause of biodiversity loss.
Canada has been affected by over a thousand alien species invasions, many with terrible effects
Dutch Elm Disease, Zebra Mussels, Knapweed

Question 18

zebra mussel

Answer 18

Native to the lakes of southeast Russia
Invasive to many countries North America, Britain, Spain and Sweden
Colonized the Great lakes
Detected in Lake Winnipeg in 2013.
Threat to native mussels
Cover the undersides of docks, boats, spread into streams and rivers nationwide.
Block pipelines, clogging water intakes of municipal water supplies.

Question 19

rusty crayfish

Answer 19

Native to Ohio River basin
Have rusty looking spots in each side of their abdomen.
A threat to the aquatic plant bed and the native species
Almost like humans clear cutting a forest.
A relatively new invader of Manitoba being initially spotted in 2007 in the Falcon Lake area

Question 20

hyper abundance

Answer 20

Native species populations increase to undesirable numbers
Where natural habitats have been disturbed
When predatory species are removed
Species culls are often used to control these population explosions

Question 21

species removal

Answer 21

Removal of species from food webs can disturb the ecosystem
The reduction of keystone species may be particularly disruptive
–For example: sea otter on the Pacific coast are overhunted  sea urchin population explodes  kelp (seaweed) habitat disappears  biodiversity is lost

Question 22

feedback

Answer 22

Feedback is an important aspect of maintaining stability in ecosystems, whereby information is returned into a system as a result of change
Feedback initiates responses that may exacerbate (positive feedback) or moderate (negative feedback) the change.
Positive feedback loop: the effect of increased temperatures in the North (polar amplification)
Negative feedback loop: the possible role of phytoplankton in global warming

Question 23

ecological restoration

Answer 23

Restoration ecology developed as a field of study, and practice, to help repair environmental damage
Examples:
Remediation of Sydney Tar Ponds
Reclamation of treeless areas around Sudbury
Efforts to reintroduce endangered species into national parks
Ecological restoration is very challenging and very costly, and there is widespread agreement that it is better to avoid ruining ecosystems in the first place rather than trying to restore them afterwards

Question 24

population

Answer 24

the number of individuals in a species

Question 25

population density

Answer 25

population calculated for a certain area, e.g., sea otters/hectare

Question 26

population dynamics

Answer 26

changes in population characteristics over time (such as birth rate and death rate)

Question 27

carrying capacity

Answer 27

The carrying capacity of an environment is the number of individuals of a given species that can be sustained in a given area indefinitely, given a constancy of resource supply and demand
Not fixed, it is a property of the ecosystem and depends on its abiotic and biotic components

Question 28

density-dependent

Answer 28

Density-dependent species have an s-shaped growth curve (higher population – lower growth rate)

Question 29

density-independent

Answer 29

Density-independent species have a J-shaped growth curve (higher population – higher growth rate)

Question 30

population growth

Answer 30

The capacity of species to increase in number is known as their biotic potential, the maximum rate at which a species may increase if there is no environmental resistance
However, different species have different reproductive strategies

Question 31

R-strategist

Answer 31

Some species are known as r-strategists, which produce large numbers of young early in life and over a short time period, but invest little parental energy in their upbringing
 e.g., insects, rodents, algae, annual plants, fish
Such species are usually small and short-lived; they are opportunists; and tend to dominate the early seral stages of the successional process
They focus on quantity of offspring

Question 32

k-strategist

Answer 32

In contrast, K-strategists focus on quality; they produce few offspring but devote time and effort to ensuring these offspring reach maturity; they tend to live longer and are larger
e.g., larger mammals, including humans
Many endangered species are K-strategists

Question 33

r marine species

Answer 33

jellyfish

Question 34

k marine species

Answer 34

white side dolphin

Question 35

r-selected species

Answer 35

High rate of population increase Opportunist species

Question 36

k-selected species

Answer 36

Low rate of population increase Competitor species

Question 37

evolution

Answer 37

over the long term, populations adapt to changing conditions through evolution, a change in the genetic makeup of the population with time
Genetic variability is required (sometimes via mutations)

Question 38

natural selection

Answer 38

leads to changes in the characteristics of a population; those individuals that have genes that allow them to be better adapted to new conditions are more successful in terms of survival and reproduction
The offspring of these individuals are also successful, and the adaptive genes become common in the population

Question 39

coevolution

Answer 39

Species may also change through coevolution, whereby changes in one species cause changes in another
e.g., a prey species evolving to be more effective in avoiding a predator, or in pollinators and flowering plants
ex) tropical orchids

Question 40

contemporary evolution

Answer 40

refers to processes that biologists have identified as occurring much more quickly as a result of human activities
54
One of the key drivers of contemporary evolution is human harvesting of prey populations
•e.g., size decline in large hunted animals

Question 41

speciation

Answer 41

Phyletic evolution is the process in which a population has undergone so much change that it is no longer able to interbreed with the original population and a new species is formed
This is the process of speciation
It can occur due to geographic isolation of populations, or adaptations of a part of a population, e.g., to a new food source
Genetic diversity helps to protect a species from environmental change and extinction

Question 42

extinction

Answer 42

Extinction is the opposite of evolution and represents the elimination of a species that can no longer survive under new conditions
Close to 99 per cent of the species that have lived on Earth are now extinct.
Speciation rate has exceeded the extinction rate in the past; however in recent times, human activities have strongly tipped the scales in favour of extinction over speciation
Extinction is not a smooth, constant process; it is punctuated by sudden, catastrophic changes

Question 43

three types of species extinction

Answer 43

Local extinction
–No longer found in a specific area
–Can still be found elsewhere
Ecological extinction
–Too few individuals left to fulfill its role in the ecosystem
Biological extinction
–No longer found anywhere on Earth