Lecture 31 - Ecology (part 2) Flashcards
What do populations have the potential to do?
to expand in size when resources are abundant and conditions are ideal
What is population size determined by in an IDEAL environment?
is determined by births, immigration, deaths, and emigration
If we ignore immigration/emigration, we can represent:
the change in population (N) over time (t) as the number of births (B) – deaths
(D)
What do ecologists like to use?
like to use models that describe per capita (per individual)
What does the per capita change in population size (rΔt) represent?
the contribution that an average member of the population makes to the number of individuals added/subtracted during a time interval
• Ie if a population of 1000 increases by 16 individuals per year, it has a
per capita change of 16/1000
• If we know the per capita change and the size of the population, we
can calculate R
How can you calculate the change at an instance of time?
using differential calculus
Change in Population =
Births + Immigrants – deaths – emigrants
Exponential growth
Populations whose members all have access to abundant food and resources grow rapidly
The resulting plot of exponential growth has a…
“J” shaped curve
“J” shaped curve
- The per capita rate of increase remains constant (and equals r)
- The number of individuals added to the population gets larger and larger per unit time
Example of exponential growth:
Population has a constant growth rate of 2 will increase by 40 individuals per unit time but will add 200 individuals when the population size is 100.
Populations with HIGHER rates of increase (r=1) will grow _____ than one with LOWER rates of increase (r=0.5)
faster
Exponential growth is a characteristic of…
populations that are introduced to new environments or in populations rebounding from a drastic event
Logistic growth
Environments have limited resources, and as populations increase, the resources decrease
Carrying capacity (K)
is the MAXimum population size that an environment can sustain
• If a population doesn’t have enough resources, birth rates decrease and the populations decline
Logistic growth models are…
sigmoidal (S-shaped), that is the population per capita growth approaches zero as K is reached
(K-N)
Number of additional individuals the environment can support
K
Carrying capacity
dN/dt=rN(K-N)/K
Fraction of K that is still available for population growth
When N less than K…
(K-N)/K is close to 1 and per capita growth rate is high (and close to r)
When N>K…
(K-N)/K is close to 0 and per capita growth rate is low
When N=K…
the population will stop growing
New individuals are added to the population most rapidly during what?
during the intermediate population sizes
Why are new individuals added to the population most rapidly during the intermediate population sizes?
- Enough breeding individuals available
* Available space and resources still abundant
So WHY does the population growth rate decrease as N approaches K?
- Birth rate DEcreases
- Death rate INcreases
- Both birth rate decreases and death rate increases
What are the assumptions that logistic models have that do not really fit real biological scenarios?
• Assumes populations can adjust instantaneously to increase density by lowering birth rates or raising death rates (there is often a delay)
- Populations will often overshoot carrying capacity temporarily
• Assumes environment doesn’t change
Community interactions are…
dynamic!
Biological community
is a group of populations of different species that live close enough to interact
Interspecific interactions
are interactions between different species
Types of Interspecific interactions:
- Competition -/-
- Predation +/-
- Herbivory +/-
- Parasitism +/-
- Mutualism +/+
- Commensalism +/0
- Altruism (facilitation) +/+ or +/0
What do species interactions influence?
the community composition
Species decline or increase abundance as…
interactions alter survival or reproductive rates of others
Interactions can also influence what?
evolution of species, changing their morphology, physiology, and behavior
What do kelp forests provide?
food and shelter for a variety of species
What can Sea urchins do?
decimate kelp forests, affecting the other members in the community
Competition benefits…
no one!
Interspecific competition
is a negative ecological interaction
- aka no one benefits
What do individuals of different species compete for?
limiting resources (resources that are required for growth and development)
Examples of Interspecific competition:
- Garden weeds compete with planted flowers for soil nutrients and water
- Grasshoppers and bison compete for grass to eat
Competitive exclusion
occurs when one species uses the resources more efficiently than the other species
What does competitive exclusion lead to?
Leads to one species being stronger and more fit (higher reproductive success) than the other species
• Eventually causes local elimination of the inferior competitor
What did G.F. Gause study & what did he find?
studied Paramecium aurelia and P. caudatum
- When grown in culture separately, grew logistically and reached carrying capacity
- When grown together, P. caudatum became extinct in the culture since P. aurelia appeared to have a competitive edge
Ecological niches determine…
resources!
Ecological niche
An organism’s ecological niche contains all of the abiotic and biotic resources a species needs to survive
What can an organism’s ecological niche include?
Can include
- temperature
- size of habitat structures (trees, branches, rocks, etc)
- food availability
- moisture
- etc
What happens if two species ecological niches are identical?
then the two species cannot coexist in the same community
• Resource partitioning allows species to coexist
• Species are able to use some, but not all of the shared niche
What does resource partitioning allow?
allows species to coexist
• Species are able to use some, but not all of the shared niche
Fundamental niches
are the niches potentially occupied by that species
Realised niches
are the portion of the niches a species actually occupies
Explain what Joseph Connell did…
removed a barnacle species residing beside another one to see if the reason for the stratification was due to interspecific competition
• It was! Chthamalus was able to colonise lower tidal zones when Balanus was removed
What can ecological niches result in?
character displacement in order to reduce competition (ex Galapagos finches)
Exploitation benefits…
only one species
Any +/- interaction is a form of…
exploitation
Predation
is a +- exploitive interaction where one species (predator) EATS another animal (prey)
Animals that eat seeds are also considered…
predators
Predators are _________ affected by humans
disproportionally
How are predators disproportionally affected by humans?
- We killed off wolves that ate our sheep (still cull wolves in BC)
- These have huge affects on the community structure
- Predator-prey relationships are very interconnected
- Higher prey abundance leads to higher predator abundance and vice versa
Predator-prey relationships are very…
interconnected
• Higher prey abundance leads to higher predator abundance and vice versa
What have prey evolved?
behavioural, mechanical, and chemical adaptations to help reduce predation
Examples of what prey have evolved behavioural, mechanical, and chemical
adaptations to help reduce predation:
- Alarm calls, Mobbing predator (birds attacking predators)
- Hiding, fleeing, forming herds/schools
- Mechanical spines (porcupines)
- Chemical excretions (skunks)
- Aposematic (bright) warning colours (poison dart frog)
- Cryptic colouration (camouflage)
- Batesian mimicry (a palatable species mimics a not-so-good one)
- Mullerian mimicry (two or more unpalatable species mimic each other, ie yellow jacket and cuckoo bee)
Herbivory
is an exploitive +/- interaction in which an organism EATS a part of a PLANT or ALGAE
Examples of herbivory:
- Many are large animals such as moose, deer, cows, elephants, bears
- Most are invertebrates such as snails, insects, beetles
Like predation, herbivory affects…
the abundance of other species
- Desert locusts can swarm and destroy vegetation, leaving severe economic loss of farmers
- Sea urchins can wipe out productive kelp forests into ocean barrens
- Beavers convert forest-bordered streams into ponds and open meadows, causing shifts in the species of vegetation present
What do herbivores have?
specialised feeding adaptations
- Chemical sensors to distinguish plant species and plant toxicity
- Specialised teeth or digestive systems for processing different vegetation types
Parasitism
is an exploitive +/- interaction in which an organism DERIVES NUTRIENTS from another organism (HOST)
____of all species are believed to be parasites
~1/3
Endoparasites (give example too)
live within the host
• Ex. Tapeworms
Ectoparasites (give example too)
feed on the external surface
• Ex. Ticks and lice
How do parasites do what they do?
- Some parasites lay their eggs in a host and the larvae hatch and feed on the living host
- Ex. Parasitoid wasps
- Some later host behaviour
- Ex. Acanthocephalan worms cause their crustacean hosts to leave protective cover and head into the open to be eaten
What is the life cycle like for parasites?
Many parasites have complex life cycles (remember Apicomplexans?), requiring 2 or more hosts
Parasitism significantly affect…
the survival of host populations
• Cause them to be weaker
- reduce reproductive output
- physical loss of features (ex fur/hair) making them susceptible to the elements
Positive interactions influence…
community dynamics
Positive interactions
(+/+ or +/0) occurs when at least one species benefits from the interaction and
neither is harmed
Mutualism
is a positive +/+ interaction (not quite symbiosis but can be used synonymously)
Examples of mutualism:
- Nitrogen fixing bacteria in legume root nodules
- Microorganisms digesting cellulose within the guts of termites and ruminant animals
- Mycorrhizae
- Endophytic fungi
- Photosynthetic algae withing corals
- Lichens!
Obligate mutualists
CANNOT survive on their own and must associate with their mutualistic partner (ex.
lichens)
Facultative mutualists
can survive without the mutualism, but benefit greatly from it
• Ie acacia-ant interaction -> will defend the tree in exchange for nectar and protective shelter
What do positive interactions involve?
- Involve the co-evolution of adaptations in both species, where changes in one species can affect the survival of the other
- Ie Many flowering plants and specific pollinators
Commensalism
is a positive +/0 interaction that only benefits one species but does NOT HARM either
Why is commensalism difficult to document in nature?
because hard to discern the close association
- Does the relationship really not harm or affect the species?
- Ie hitchhiking algae on snail shells gain a new place to grow but many actually cause a very slight decrease in reproductive success in the snails….but is it counteracted by the addition of new camouflage?
Where does commensalism often involve on?
Often involves on species obtaining food exposed by the other
- Cattle egrets and cowbirds gain abundant food source when bison, cattle, etc disturb and flush out ticks and other insects
- Following these animals provides the birds with ample food and little foraging effort
- Can affect the cattle. Bison etc too…..birds wil sometimes each the ectoparasites directly off their bodies
Facilitation (altruism)
is a positive +/+ or +/0 interaction where species may not have a direct contact in the symbiosis
Example of Facilitation (altruism):
Ex Juncus gerardi makes the soil In salt marshes more hospitable, which other plant species can use later
• Shades the soil, preventing salt buildup due to surface evaporation
• Also transports oxygen to the soil
• Removing Juncus from the area resulting in a 50% decline in plant species present
