Ch 12 eco notes (you still need to go in book this is just info from slide)

Offspring number vs. size

Organisms have access to limited energy and resources.

Principle of allocation – if organisms use energy for one function (e.g., growth), the amount of energy available for other functions is reduced.

Leads to trade-offs between functions.

•Trade-off between number and size of offspring

Egg size and number in fish

Fish show more variation in many life-history traits than any other group of animals.

Turner and Trexler studied relationship between egg size and egg number (fecundity) and extent of gene flow among darter populations.

•Found larger species produce more eggs

•Found that darters producing larger eggs tend to produce fewer eggs

Darter size and egg size and number

The females of larger darter species produce more eggs

Darter species that produce larger eggs lay fewer

Effects on gene flow

Found a negative relationship between egg size and gene flow.

•Larvae hatched from large eggs are larger, drift less, disperse shorter distances

•Populations producing fewer, larger eggs are more isolated genetically

Found a positive relationship between gene flow and number of eggs produced.

Seed size and number in plants

•Plants vary widely in seed production

•From many small seeds to few large seeds

•Two factors may influence seed size and production

•Plant growth form

•Dispersal mode

(plants that produce larger seeds produce fewer.)

Plant growth form and seed size

Westoby et al. recognized four plant forms.

Graminoids: grass and grass-like plants

Forbs: herbaceous, non-graminoids

Woody plants: woody thickening of tissues

Climbers: climbing plants and vines

Found that woody plants and climber produced 10x the mass of seeds than either graminoids or forbs

Plant dispersal mode and seed size

Westoby et al. recognized six seed dispersal strategies:

•Unassisted, adhesion-adapted, wind, ants (seeds with elaiosome), vertebrates (seeds with aril), scatterhoarded (seeds gathered and stored in caches)

Unassisted dispersers had the smallest seeds

Animal dispersed seeds were the largest

•Scatterhoarded seeds larger than ant- or vertebrate-dispersed

Causes of variation in seed size

•Plant growth form and dispersal mode associated with seed size variation.

•Small plants producing large number of small seeds appear to have an advantage in areas of high disturbance.

•Plants producing large seeds are constrained to producing fewer seedlings but are more capable of surviving environmental hazards.

Seed size and seedling performance

Jakobsson and Eriksson found seed size variation explained many differences in recruitment success.

•Larger seeds produce larger seedlings and were associated with increased recruitment.

(larger seedlings grew from larger seeds)

Tree seed size and seedling performance

Seiwa and Kikuzawa found larger tree seeds produced taller seedlings.

•Energy reserve boosts seedling growth.

•Rapid growth helps seedling penetrate thick litter layer.

(tree seedlings that grew from larger seeds were taller)

Adult survival and reproductive allocation

Relationship between probability of yearly survival and age of first reproduction and the energy allocated (reproductive effort)

•If adult survival is lower, organisms begin reproducing earlier.

-Allocate large part of energy budget.

•If adult survival is higher, organisms defer reproduction

-Allocate small part of energy budget.

Life history variation among species

Shine and Charnov pointed out vertebrate energy budgets are different before and after sexual maturity.

•Before - maintenance and growth

•After - maintenance, growth, and reproduction

Individuals delaying reproduction will grow faster, reach a larger size, and have a higher reproductive rate

Life history variation in snakes and lizards

•Shine and Charnov found snakes and lizards with higher survival rates reached age of reproductive maturity later.

•Gunderson found fish with higher adult mortality showed earlier age of maturity and higher relative reproductive effort.

Life history variation within species

Bertschy and Fox studied influence of adult survival on pumpkinseed sunfish life history.

•Found significant variation in most life history characteristics across study lakes.

•Data suggest that population with higher adult survival mature at a greater age.

•Found when adult survival is lower relative to juvenile survival, natural selection favors allocating more resources to reproduction.

(pumpkinseed sunfish populations with higher ratios of adult to juvenile survival showed lower reproductive effort)

Life history classification. r and K selection (MacArthur and Wilson)

r selection (r is per capita rate of increase)

favors high population growth rate

strongest in species colonizing new or disturbed habitats

K selection (k is carring capacity)

Favors efficient resoue use

Prominent when populations are near K

(Pianka identified r and K selection as ends of continuum; most organisms are in between)

r and K : Fundamental contrasts

Plant life histories

Grime (1977, 1979) proposed two variables most important in exerting selective pressures in plants:

•Intensity of disturbance and intensity of stress

Grime contrasted 4 environmental extremes

•Low disturbance-low stress (has plants)

•Low disturbance-high stress (has plants)

•High disturbance-low stress (has plants)

•High disturbance-high stress (no plants)

Matching plant life histories to environments

Ruderals (highly disturbed habitats)

•Grow rapidly and produce seeds quickly and in large numbers

•similar to r-selection

Stress-tolerant (high stress, no disturbance)

•Grow slowly, conserve resources

•similar to K-selection

Competitive (low disturbance, low stress)

•Potential to grow well but eventually compete with others for resources

Opportunistic, equilibrium and periodic life histories

Winemiller and Rose (1992) proposed new classification scheme for fish life histories.

•Based on age of reproductive maturity (⍺ ), juvenile survivorship ( l_x ) and fecundity ( m_x )

•Opportunistic, equilibrium, and periodic life history strategies

•Opportunistic shares some features with r selected and ruderal species

•Equilibrium shares some features with k selected

Fish life history classification

opportunistic life history combines low juvenile survival (lx), low fecundity (mx), and early maturity (geek a/alpha)

The periodic life history combines low juvenile survival, high fecundity, and late maturity.

The equilibrium life history combines high juvenile survival, low fecundity, and late maturity.

Lifetime reproductive effort and relative offspring size:
Two central variables?

Charnov et al. created life history classification.

Uses a few key life history features converted to dimensionless numbers

•Relative size of offspring: 1/m

•Proportion of body mass allocated to reproduction per unit time times adult lifespan: C∙E

Removing influences of time and size makes similarities and differences between groups easier to identify

(birds mammals, and lizards occupy well-separated regions in Charnov’s life history plane.)

Applications: Climate change and timing of reproduction and migration

Seasonal change affects availability of food and other resources.

•Timing is critical for reproductive success.

Many historical records of seasonal change.

Historical records allow study of the timing of ecological events (phenology) in comparison to factors such as climate and weather.

Altered Plant Phenology

•Miller-Rushing and Primack found a relationship between increasing temperatures and earlier blooming time in 43 species of plants.

•Animals are adjusting as climate warms.

•Vitale and Schlesinger found that migratory birds are arriving significantly earlier in the spring.

•Short-distance migrants have greater shifts in timing.