Summary Biology A2 level 'population size and ecosystems' notes (WJEC)
13 views 0 purchase
Course
Population size and ecosystems
Institution
WJEC
Book
WJEC Biology for A2: Study and Revision Guide
Biology A level 3.5 population size and ecosystems. These notes were formulated using class notes, the WJEC study guide and past papers. These notes helped me to achieve an A* at A level biology!
Biology A2 level 'variation and evolution' notes (WJEC)
Biology A2 level 'inheritance' notes (WJEC)
Biology A2 level 'sexual reproduction in plants ' notes (WJEC)
All for this textbook (8)
Written for
A/AS Level
WJEC
Biology
Population size and ecosystems
All documents for this subject (3)
Seller
Follow
atwellkate
Content preview
3.5 Population size and ecosystems
Populations
Factors affecting population size
● Population size = birth rate + immigration - death rate + emigration
○ Population = total number of organisms of a single species interbreeding within a
habitat
■ Habitat - physical place where an organism lives
○ Birth rate - number of new individuals derived from reproduction per unit of time
○ Immigration - movement of individuals into a population
○ Death rate - number of individuals dying per unit of time
○ Emigration - movement of individuals out of a population
● Lag phase - period of slow growth
○ Time to reach sexual
maturity and gestation
● Exponential log phase
○ Numbers increase
logarithmically as there
are no limiting factors
○ Cannot be maintained
indefinitely as biotic and
abiotic factors reduce
growth
■ Biotic factors - a
living factor that
may influence a
population e.g.
predator or pathogen
■ Abiotic factors - a non-living factor that may influence a population e.g.
soil pH, light intensity, temperature
● Stationary phase
○ Population has reached its maximum size
■ Carrying capacity - the maximum number to which a population can be
sustained in a given environment i.e. maximum population size an
environment can sustain
■ Birth and death rates are equal
○ Numbers fluctuate around this number in response to environmental changes
■ Negative feedback - occurs in an equilibrium where the corrective
mechanism is in the opposite direction to the direction of change
● e.g. Predator-prey interactions - if prey numbers decrease ⇾
predator numbers decrease ⇾ prey numbers increase
, ● Death phase
○ Death exceeds births ⇾ population size
decreases
○ Factors that have reduced population
growth become more significant
○ A population crash is a sudden
decrease in population numbers
■ Occurs when a population
greatly exceeds its carrying
capacity
■ After a population crash the
carrying capacity for that
environment will be lower, due to damaged caused by overpopulation
Strategies for population growth
● Fugitive species
○ Cannot tolerate competition
○ Increase numbers by rapid reproduction and effective dispersal mechanisms ⇾
invade new environments rapidly
○ E.g. algae & weeds
● Equilibrium species
○ Control population by competition within a stable habitat
○ Have a one-step growth curve (sigmoid, S-shaped) rabbits and bacteria
populations show this kind of growth
Calculating population increase from a graph
Growth rate = growth
time
Growth rate = antilog10 large population - antilog10 small population
number of days
Growth rate = 105 - 102 ⇾ 19,980 per day
5
Antilog = [shift] [log] [number]
Density-dependant & density-independent factors
Density-dependant
● Their effect increases as the density of the population increases
● Biotic factors
○ Disease is more easily spread
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller atwellkate. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $6.47. You're not tied to anything after your purchase.
