Ecology - Week 11 Flashcards
Conservation Plan:
Why does removal of a species have to be carefully considered?
it may not always be a good idea to remove them, as removal of this species may affect other species in the food web
What is survivorship?
proportion of individuals surviving
Population Dynamics:
What are the factors that regulate changes in population size?
- births
- deaths
- immigration: moving into a population
- emmigration: moving out of a population
What is carrying capacity?
max # individuals a habitat can support over sustained period of time
How is per capita growth rate (r) calculated?
(birth rate – death rate) / population
Describe the population when the per capita growth rate is HIGH.
population will grow quickly
Describe the population when the per capita growth rate is LOW.
population will grow slowly
Describe the population when the per capita growth rate, r > 0.
population size will increase
Describe the population when the per capita growth rate, r > 0, and is constant.
will see exponential growth
When is population size increasing?
r > 0
When is population size decreasing?
r < 0
When is population size not changing?
r = 0
Describe per capita growth rate (r) in exponential growth.
- r is constant
- r is density-independent
Describe per capita growth rate (r) in logistic growth.
- r is decreasing to 0
- r is density dependent
What is intrinsic per capita growth rate (r max)?
rate at which population grows when it is NOT limited by
- competition over resources
- predation
- disease
- environmental disasters
(first 3 are often related to population density, last one usually isn’t)
Does r max vary between species?
yes
What factors contribute to a LOW intrinsic per capita growth rate?
- long generation times (individuals take a long time to reach reproductive age)
- few offspring produced per individual (low per capita birth rate)
- relatively high per capita death rate compared to per capita births
What factors contribute to a HIGH intrinsic per capita growth rate?
- short generation times (individuals reach reproductive age quickly)
- many offspring produced per individual (high per capita birth rate)
- relatively low per capita death rate compared to per capita births
What happens once population reaches carrying capacity?
r = 0
What happens in a logistic growth curve plot?
per capita growth rate starts out equal to the intrinsic growth rate, but then starts to decrease as it approaches the carrying capacity
Is the actual growth rate or intrinsic growth rate bigger?
actual growth rate < intrinsic growth rate
What happens in an exponential growth curve plot?
per capita growth rate = the intrinsic per capita growth rate throughout
What is the maximum growth rate in a logistic growth curve plot?
carrying capacity
What is the maximum growth rate in a logistic growth curve plot?
highest r
What is an ecological disturbance?
any event that removes biomass from a community
What is a population?
group of all the individuals of the same species, in a given area
What is a community?
all of the populations that interact with one another, in a given area
What is biomass?
mass of living organisms
What can we calculate the biomass of?
- single individual
- whole population
- whole community
- planet
What is succession?
development of a community
Which factors will be most important in determining the composition of a community immediately following a disturbance?
abiotic factors
What happens following a disturbance?
- density of organisms will be reduced (and, in many cases, biodiversity will also be reduced)
- all else being equal, we should expect the number of interactions between organisms to be fewer after a disturbance compared to before
- in particular, we should expect competition for particular resources (ie. space, light) to be less intense
Describe the conditions of early successional communities.
harsh abiotic conditions
- soil with few nutrients and little water retention
- little shade, little protection from the elements (wind, sun, rain), etc.
Describe the conditions of late successional communities.
resources (nutrients, water) and shelter (shade, protection from wind and erosion) will be more plentiful, however, so will competition for those resources and niche space
however, that’s not to say that all biological interactions will be negative!
ie. taller plants shelter smaller plants from the sun and other elements
ie. nitrogen-fixers provide non–nitrogen-fixers with nitrogen
ie. forest provides habitat for animals who will assist with seed dispersal and germination
What do we focus on when talking about early successional vs. late successional species?
plants
however, we can also classify certain animal species as being early vs. late successional
Before all else, what will determine whether or not a species is found at a particular location?
its ability to disperse
What is a realized niche?
related to its ability to outcompete other species
if it is a strong competitor, it will likely have a larger realized niche in the presence of a competitor
Describe the importance of “before all else” in the question:
Before all else, what will determine whether or not a species is found at a particular location?
- in the end, it may not matter whether or not a species is capable of living in a particular location if it can’t disperse there
- furthermore, a species may be temporarily found at a particular location because it happened to disperse there, even if it is not expected to survive at that location (ie. there is a difference between simply being found at a location, and being established at that location)
- an organism’s fundamental niche, realized niche, and ability to compete with other species are all important factors that will influence whether or not it is able to survive at a particular location
- however, these are also things that will depend heavily on what other organisms are already present at that location
- for example, fireweed would grow well in an area immediately following a forest fire (when there is little competition and plenty of light), but would struggle in the same area after other species had established themselves
Although humans may find the higher productivity and biodiversity of a late successional community appealing, why would it be misleading to think of a late-succession community as being an “end goal”?
- climax communities may not be able to sustain themselves indefinitely, given the intense competition for resources
- depending on the frequency of different types of disturbances, communities are expected to cycle through the process of succession
- furthermore, even after communities that have reached a high density of species, there may still be cycling (e.g., nitrogen-depleting species being replaced by nitrogen-accumulating species, which are then replaced by nitrogen-depleting species)
Why might some areas start to recover sooner than others after a disturbance?
in some cases, it may be because these areas suffered slightly less damage
however, another important factor is the ability of plants to disperse to a particular location – plants will be able to disperse to areas that are closer sooner than they are able to disperse to areas that are further away
Describe primary succession.
no soil
disturbances:
- volcanic eruptions
- glaciers
- floods
- landslides
Describe secondary succession.
soil remains
disturbances:
- forest fires
- logging
- construction
- farming
Conditions at the beginning of primary succession are incredibly harsh – not even soil is present, but how can an environment possibly become a productive community?
primary succession, made possible by lichens
What are lichens?
the result of a symbiotic relationship between fungi and one or more of algae and different types of bacteria
fungi and algae/bacteria have adapted to one another (ie. they are co-evolved), and are dependent upon one another
Why will lichens always be the first organisms present at the beginning of primary succession?
many lichens are capable of growing without soil (some are even capable of growing without any substrate at all)
Lichens are incredibly diverse. Give some examples of lichens.
- lichens that contain algae are capable of fixing carbon (ie. undergoing photosynthesis)
- lichens that contain cyanobacteria are capable of fixing both nitrogen and carbon
How can lichen make an environment possibly become a productive community?
once several layers of dead lichens (ie. organic matter) have accumulated, the substrate will begin retaining moisture
this allows mosses to move in
the combination of mosses and other accumulating organic matter forms a thin soil
Describe pioneer species.
- high dispersal
- weedy/fast growing, short generations
- tolerant of harsh conditions
Describe climax species.
- low dispersal
- good competitors, long-lived
- require favourable conditions
