Class Notes (922,111)
CA (542,723)
UTSG (45,887)
BIO (2,271)
BIO120H1 (1,175)
Lecture 7

Lecture 7 & 8

7 Pages
101 Views

Department
Biology
Course Code
BIO120H1
Professor
Ingrid L.Stefanovic

This preview shows pages 1-2. Sign up to view the full 7 pages of the document.
Lectures 7 & 8 22:10
Partial Taxonomy of Species Interactions
Types of Interactions:
Consumer Resource (+/-)
Predator-prey
Plant-herbivore
Host-parasite
Competition (-/-) as one individual gets more, another gets less)
Mutualism (+/+) species benefit each other
Foci of Study:
Population dynamics (effects on numbers)
Evolutionary dynamics (adaptation, co-evolution)
Interspecific Competition:
Basic model: Lotka-Volterra equations for two species competing for resources
Simple extension of logistic equation:
Logistic already has braking term for intra-specific variation
Both species must inhibit own growth more than it inhibits growth of competitor;
otherwise, competitor drops in population and allows other species to grow
Alphas must be smallish (share less resources)
(See lecture slides for equations): know the equations and the meanings of the terms
Possible Outcomes of L-V competition:
Expect now to solve for N1 and N2 as f(t), but.
Instead, specify 4 possible equilibria:
The two species may stably coexist
Species 1 may always win (N1=K1, N2=0)
Species 2 may always win (N2=K2, N1=0)
Identity of winner may depend on starting Ns
Outcomes depend on values of Ks and as (small alphas mean less sharing of
resources = makes it easier for species to coexist)
Coexistence requires both species to inhibit their own growth more than they inhibit
each others
Can expand to consider n species
(Be able to write L-V equations and explain what the terms are)
Law of Competitive Exclusion
Complete competitors cannot coexist
Will consider this later, under niche theory
www.notesolution.com
L-V models formed core of ecological theory. How do they relate to the real world?
Experiments by Gause (1930s)
Good description of competition by protozoa in artificial culture vessels; saw both
stable coexistence and competitive exclusion: can be unstable
Predator-prey strongly tended to be unstable (predators eat up all the prey, then
starve) unless habitat complexity added)
(View lecture slides for graphs of Gauses data.)
How are competitive effects manifested in nature, rather than in containers?
Competitive exclusion is less likely to go to completion
…but abundances can be drastically affected
and distributions in space altered.
Biological effects interact with physical effects
Natural selection tends to favour higher competitive ability.
E.g., lynx hare cycle. Not as simple; the plant quality available to the hares falls
when there are many hares. Social stresses (endocrine collapse) in overcrowded hare
populations.
Models of Mutualisms?
Not as much work on population dynamics
L-V type models blow up, Ns grow toward infinity; something outside the
mutualism must limit numbers
So, more attention has focused on evolutionary aspects…
Although losses of mutualists can cause population declines.
Connecting L-V competition to niche theory, 1960s to 1970s:
Assume competitive exclusion is the important force, so coexistence requires
differentiation
How to measure differentiation? Ecological niche concept, can incorporate abiotic
and biotic factors
Leap of faith: competition alphas could be represented by niche overlap measures
Emerging theory: community composition determined by features that allow
coexistence: limiting similarity; resource partitioning, assembly rules, character
displacement
Niche partitioning, the inspirational case:
Insectivorous warblers many similar species breed in coniferous forest. Alphas
should be high (sharing of resources should be high). How do they coexist?
Niche overlap measures ecological similarity
www.notesolution.com

Loved by over 2.2 million students

Over 90% improved by at least one letter grade.

Leah — University of Toronto

OneClass has been such a huge help in my studies at UofT especially since I am a transfer student. OneClass is the study buddy I never had before and definitely gives me the extra push to get from a B to an A!

Leah — University of Toronto
Saarim — University of Michigan

Balancing social life With academics can be difficult, that is why I'm so glad that OneClass is out there where I can find the top notes for all of my classes. Now I can be the all-star student I want to be.

Saarim — University of Michigan
Jenna — University of Wisconsin

As a college student living on a college budget, I love how easy it is to earn gift cards just by submitting my notes.

Jenna — University of Wisconsin
Anne — University of California

OneClass has allowed me to catch up with my most difficult course! #lifesaver

Anne — University of California
Description
Lectures 7 & 8 22:10 Partial Taxonomy of Species Interactions Types of Interactions: Consumer Resource (+-) Predator-prey Plant-herbivore Host-parasite Competition (--) as one individual gets more, another gets less) Mutualism (++) species benefit each other Foci of Study: Population dynamics (effects on numbers) Evolutionary dynamics (adaptation, co-evolution) Interspecific Competition: Basic model: Lotka-Volterra equations for two species competing for resources Simple extension of logistic equation: Logistic already has braking term for intra-specific variation Both species must inhibit own growth more than it inhibits growth of competitor; otherwise, competitor drops in population and allows other species to grow Alphas must be smallish (share less resources) (See lecture slides for equations): know the equations and the meanings of the terms Possible Outcomes of L-V competition: Expect now to solve for N1 and N2 as f(t), but. Instead, specify 4 possible equilibria: The two species may stably coexist Species 1 may always win (N1=K1, N2=0) Species 2 may always win (N2=K2, N1=0) Identity of winner may depend on starting Ns Outcomes depend on values of Ks and as (small alphas mean less sharing of resources = makes it easier for species to coexist) Coexistence requires both species to inhibit their own growth more than they inhibit each others Can expand to consider n species (Be able to write L-V equations and explain what the terms are) Law of Competitive Exclusion Complete competitors cannot coexist Will consider this later, under niche theoryion.com
More Less
Unlock Document


Only pages 1-2 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


OR

Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit