Transcript POPULATIONS RESPOND TO PRESSURES

POPULATIONS RESPOND TO
PRESSURES
• Population Growth is Limited:
– Birth, Death, Immigration & Emigration
– Limiting Factors
– Effects of Population Density
• Populations have Distinct Reproductive
Survival Strategies:
– Reproduction is necessary for the survival of a
species.
– Scientists observe patterns in the reproductive
strategies used among species
• Opportunist strategies & Competitor strategies
Birth/Death/Immigration/Emmigration
• Population Change =
– (birth + immigration) – (death + emigration)
• Immigration= movement of individuals into a population
(winds blowing plant seeds in)
• Emigration= movement of individuals out of a population
(some leave if resources get scarce)
• If a storm comes, a flock of seagulls may fly into a city dump
and add to the existing population. Raccoons have been
eating the seagull eggs there, so the immigrating birds could
help stabilize the population or increase it (especially if some
of the raccoons moved away)
Limiting Factors
• When birth rate is much higher than death rate, population
grows rapidly; eventually, population will stop growing due
to lack of resources in habitat.
• Limiting Factor= prevents the continuing growth of a
population in an ecosystem.
– Abiotic (non-living) factors = air, light, water.
– Biotic (living) factors = other organisms in same habitat
or same species in same area.
• Competition may occur between different populations or
same populations in a habitat. (Deer growth in our area is
making resources scarce for entire population)
Population Density Effects
• Density-dependent Factor= limiting factor affecting
a population when density is high (competition for
food, disease-spreads easier in crowds). These have
a greater effect as population grows.
• Density-independent Factor= limiting factor having
same effect on population whether high or low
density. (Freezing temp., natural disasters, famine-no
food available)
Opportunist Strategies
• Opportunists: species that reproduce rapidly if their
population falls below carrying capacity. Have:
– Short life span usually & ability to reproduce large
quantities of offspring.
– Population size changes often & live across many areas.
• Include: algae, dandelions, bacteria, & insects. All reproduce
quickly & move across area quickly.
• Can adapt quickly to environmental changes.
Competitor Strategies
• Competitor: species with adaptations that allow them to
remain at or near their carrying capacity for long period of
time (different from other competitor who struggles with
another to get resources).
• Often live longer & have fewer offspring (elephants &
saguaro cacti). Offspring usually take longer to develop into
adults so are cared for by parent longer.
• Not spread out over wide area as much, but more of offspring
survive to reproductive age.