Download LIFE HISTORY STRATEGIES

What is Ecology?
Scientific study of the interactions of
organisms with their abiotic and biotic
environments...
...in order to understand the distribution
and abundance of organisms in space and time.
Fields of Ecology
Organismal Ecology (physiology, behavior)
Population Ecology (life history strategies, demography, population growth)
Community Ecology (species interactions, biodiversity)
Ecosystem Ecology (energy & nutrient flow, landscape ecology)
Population Ecology
• A population is a group of individuals of the same
species that live in a particular area and have the
potential to interbreed.
Flock of Starlings at Dusk – U.K.
Life History Characteristics
• Growth
• Change of form
• Dispersal
• Timing of reproduction
• Size at birth or germination
• Number and size of offspring
• Age at death
Life History - Growth
• Growth – for at least part of their life history,
all organisms grow by assimilating energy and
nutrients – final body size species-specific.
Life History – Change of Form
• Change of form - many organisms have
dramatically different forms or stages in their
life cycle.
Life History - Dispersal
• At some time in their lives, most organisms go
through dispersal – enhances reproductive success.
Belding’s Ground Squirrel
Spiders
Milkweed
Life History Characteristics
• Growth
• Change of form
• Dispersal
• Timing of reproduction
• Size at birth or germination
• Number and size of offspring
• Age at death
LIFE HISTORY STRATEGIES (LHSs):
Patterns of lifespan and reproduction
that characterize a species.
LHSs are a result of natural selection,
which acts on individuals, NOT species
Individuals that have a life history that
maximizes fitness will be favored by
natural selection…
…thus, particular patterns of survival
and reproduction will eventually be
shared by all members of a population.
Three Main Life History Strategies:
1) Survivorship
2) Maturity
3) Reproductive Output
3) Reproductive Output
a) Parity
# reproductive episodes in lifetime
Mayfly
Salmon
Agave
Semelparous species
Iteroparous Species
3) Reproductive Output
a) Parity
b) Fecundity
# offspring per reproductive episode
elephants
rodents
spiders
3) Reproductive Output
a) Parity
b) Fecundity
c) Parental Investment
Energetic effort put into offspring:
i) Size of offspring
• Some plants produce a large number of small seeds, ensuring that
at least some of them will grow and eventually reproduce.
•
Other types of plants produce fewer large seeds that provide a large
store of energy that will help seedlings become established.
General Relationship between Offspring Size
and Number of Offspring
Many
Number
of
Offspring
Few
Small
Large
Offspring Size
3) Reproductive Output
a) Parity
b) Fecundity
c) Parental Investment
Energetic effort put into offspring:
i) Size of offspring
ii) Parental care
LHS of a hypothetical “super-organism”?
Real LHSs are compromises in the
allocation of energy!
Reproductive Trade-offs:
a) Reproduction vs Future Survival
Reproduction vs Survival (Mortality)
How does caring for offspring
affect parental survival in kestrels?
Parents surviving the following winter (%)
100
Male
Female
80
60
40
20
0
Reduced
brood size
Normal
brood size
Enlarged
brood size
Fig. 53-8
Reproductive Trade-offs:
a) Reproduction vs Future Survival
a) Reproduction vs Future Growth
b) Current vs Future Reproduction
Annual Meadowgrass
Reproduction vs Future
Growth
Current vs Future
Reproduction
Particular combinations of LHSs often
favored in particular body sizes…
…but there are always exceptions to the rule!
Big Brown Bat (Eptesicus fuscus)
Baby bat
Longer lifespan (14 yrs) and lower fecundity (1-2)
than expected for a mammal of that size (small)
A few, large offspring.
Parental care in carrion beetles;
very unusual for an insect.
“Octomom”
LHSs characterize species, but can also be
somewhat flexible – different populations
can adapt to different environmental
conditions…
e.g. Fat-tailed Dwarf Lemur
Pop 1: dry forest,
long torpor (6-7 months):
Fewer, smaller litters.
Pop 2: rainforest,
shorter torpor (4-5 months)
and higher mortality rates:
More frequent, larger
litters.
Trade off between longevity
and number of offspring:
Long life span selects for low reproductive investment.
Short life span selects for high reproductive investment
DEMOGRAPHY
The study of birth and death processes
that determine growth and age structure
of a population.
Each age class of a population has an expected:
Mortality rate
Fecundity rate
Demographic characteristics can be represented in:
1) Life Tables
- summarize deaths and/or births
in different age classes of a population
a) Conventional life table
Demographic characteristics can be represented in:
1) Life Tables
- summarize deaths and/or births
in different age classes of a population
a) Conventional life table
b) Diagrammatic life table (flow diagram)
2) Survivorship Curves
Number of survivors (log scale)
1,000
I
100
II
10
III
1
0
50
Percentage of maximum life span
100
Fig. 53-6