Download lecture 15 ch 10 life histories and evolution

LECTURE 08 CH 10 LIFE HISTORIES AND EVOLUTION
Life history: lifetime scheduling of resources and time to maximize fitness
Search for set of rules for traits affecting survival and reproduction and favored by
natural selection
Evolutionary context; life history traits are molded by natural selection
How to study life history evolution?
Explore variation in traits by comparative methods (not absolutes);
By experimentation
Life histories vary along a slow-fast continuum
Slow: (K-selected species) in persistent habitats; near carrying capacity
slow development
delayed maturity
large adult size
low reproductive rate
high parental investment/offspring low mortality
long life
low dispersal
Fast (r-selected species) in temporary habitats; much pop. growth potential
Opposite of slow
Resource and time allocation
Alternative pathways:
Immediate reproduction
Delayed reproduction: resources into growth – enhance competitive ability
resources into maintenance – enhance survival
Tradeoffs
Resources are finite
Resolution of conflicting demands for resources
Variation in one trait is often (negatively) correlated with another trait
1) Age of Maturation (when first reproduce?)
Benefit of early reproduction = immediate fitness gain; short generation time
Benefit of delay = age-related gains in fecundity from greater growth or experience
Cost of delay
risk of mortality before reproduce
tradeoff of survival and reproduction
reduced fecundity at later ages
Reproductive value: a product of probability of survival and future reproduction
Selection acts most strongly on age class with highest RV
Growth vs fecundity
If indeterminate growth, fecundity is related to body size
Increased fecundity reduces growth and thus fecundity in future
Short-lived species emphasize fecundity over growth
High extrinsic adult mortality favors increased reproduction now
at expense of adult survival and future reproduction
Long-lived species emphasize growth over immediate fecundity
Species with high adult survival mature later than those with low adult survival
2) Fecundity (How many offspring per reproductive bout?)
Fecundity vs. offspring survival
Fecundity vs. parental investment per offspring
Seed size vs. seed number tradeoff
Clutch size vs. number of offspring parent can feed
Variation in fecundity among species is huge
3) Parity (How many times reproduce per lifetime?)
Semelparous (monocarpic): once
Iteroparous (polycarpic): repeated
If semelparous, at what year? Annual, biennial, long-lived
Hypotheses about what favors semelparity?
Pay-off for reproduction highly variable but favorable conditions predictable from
environmental cues
Pollinators attracted to massive display
Seed predators satiated by many seeds
Preparation for reproduction extremely costly
What favors iteroparity?
Low current reproduction results in maintaining high future reproduction
Annual vs. biennial vs. perennial
How much fecundity is required so number of offspring of
annual = perennial over its lifetime?
Cole’s paradox: Fa = Fp +1
Solution: Fa = Fp + Survivaladult/ Survivaljuveinile
If high Sadult requires very large Fa; favors perennial
If low Sadult requires less large Fa; favors annual
How high fecundity is required for delayed semelparity = iteroparity?
Fdelayed > (Survivaljuvenile Fannual) no. years delay
Proportion in flora: Biennial<<<Annual<<Perennial
4) Aging and lifespan
Senescence: decline in physiological function with age
: causes decline in fecundity and survival
Strength of selection on senescence varies with mortality rate
If high mortality and few reach old agelittle selection for mechanisms to
prolong life
Why does aging vary?
Subject to natural selection and evolutionary modification
Strength of selection is less on traits expressed at progressively later ages