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Chapter 7

BIOB50 Chapter 7 Review


Department
Biological Sciences
Course Code
BIOC50H3
Professor
Marc Cadotte
Chapter
7

Page:
of 11
BIOB50 Ecology
Chapter 7 Life History
Nemo Grows Up: A Case Study
-offspring produced by different organisms vary
-grass plants produce seeds that are buried in soil until conditions are right for germination
-sea star produces thousands of microscopic eggs that develop adrift in the ocean
-rhinocero produces a calf that develops in her womb for 16-18 months
require more than a year of care before it becomes fully independent
-clownfish spend entire adult lives in a single sea anemone
-mutually beneficial relationship between clownfish & anemone
-anemone protects clownfish by stinging predators
-clownfish help anemone by eating/ driving away its predators
-2 to 6 clownfish live in a single anemone
they are usually not related to one another, not family members
-interact based on a strict pecking order based on size
-largest fish is a female
-second largest is the breeding male
-remaining fish are sexually immature non-breeders
-if female dies, breeding male undergoes growth spurt & changes sex to become a female
largest non-breeder increases in size & becomes new breeding male
-breeding male mates with female & cares for fertilized eggs until they hatch
-juvenile fish find another anemone to habit
-enter an anemone if there is room, otherwise get rejected by resident fish
-life cycle with expulsion, hierarchy & sex change
Introduction
-life history is record of major events related to its growth, development, reproduction & survival
-ex. age & size at sexual maturity, amount & timing of reproduction, survival & mortality rates
-timing & nature of life history traits are products of adaptation to the environment
Life History Diversity
Individuals within species differ in their histories
-life history strategy of species is overall pattern in timing & nature of life history events
averaged across all individuals in species
-ex. Homo sapiens
-women typically have one baby at a time
-reproduction usually occurs between ages of 15 & 45
-life history strategy is shaped by way the organism divides its energy& resources between
growth, reproduction & survival
-difference between how individuals divide energy are due to genetic variation &/or difference in
environmental conditions
Genetic differences
-genetically influenced traits are those that are more similar in families than between them
-ex. siblings are similar in appearance & reach similar adult heights & weights
Blue grass
-life history traits are similar among sibling plants
-ex. age at first reproduction, growth rate, number of flowers produced
-natural selection acts on heritable variation in life history traits
-life history is optimal & adapted to maximize fitness
-fitness: genetic contribution of organism’s descendents to future generations
-no life history results in unlimited production of descendants
-constraints prevent evolution of perfect life history
involve ecological trade-offs in which an increase in performance of one function reduce
performance of another
-ex. reproduction vs. growth/ survival
-life history is optimal in the sense of maximizing fitness subject to constraints
Environmental differences
-phenotypic plasticity is when a single genotype produces different phenotypes under different
environmental conditions
-life history traits show some degree of plasticity
-ex. different growth rate depending on temperature
-changes in life history translate into changes in adult morphology
-slower growth in cool condition leads to smaller adult size & different shape
-allocate more biomass to leaf growth relative to sapwood production in cool condition
sapwood is newly formed layers of wood that function in water transport
-allocation is relative amounts of energy/ resources that organism devotes to different functions
-desert trees are shorter & squatter, with fewer branches
have lower photosynthetic rate & consume less carbon dioxide due to fewer leaves
-phenotypic plasticity that responds to temperature variation produces a continuous range of
sizes
-in some phenotypic plasticity, a single genotype produces discrete morphs (types), with few or
no intermediate forms
2 morphs of spadefoot toad:
1) Omnivore morph
-feed on detritus & algae
2) Carnivore morph
-feed on shrimp & tadpoles
-different body shapes between the two result from differences in relative growth rate
-carnivores have bigger mouths & stronger jaw muscles
-omnivores tadpole can turn into carnivores when fed on shrimp & tadpole
-proportion of omnivore & carnivore morphs is affected by food supply
-carnivore tadpoles grow & metamorphose before ponds dry up
are favoured in ephemeral ponds
-omnivores are favoured in ponds that persist longer
metamorphose in better conditions leads to better chances of survival as juvenile toad
-in toad, relative growth of jaw & rest of the body determine whether it is carnivore or omnivore
-in pine, relative growth rates of leaves & sapwood determine body shape
-allometry is differential growth of body parts that results in a change in shape/ proportion with
size
-adaptation must be demonstrated rather than assumed
-supported with evidence by comparing the survival & reproductive rates of different types of
organism
-phenotypic plasticity is ability to produce different phenotypes in response to changing
environmental conditions increases fitness of individuals
-phenotypic plasticity can be simply physiological response, not adaptive response shaped by
natural selection
-ex. changes in growth rate due to temperature
-chemical reactions are slower at lower temperature
Mode of reproduction is a basic life history trait
-evolutionary success is determined by successful reproduction
-mechanisms for reproducing include asexual splitting, mating rituals & pollinating system
Asexual reproduction
-binary fission is dividing in half
-all prokaryotes & many protists reproduce asexually
-transmission of entire genome
Coral
-founding polyp is sexually produced
-coral colonies then grow by asexual reproduction
-each polyp is genetically identical copy (clone) of founding polyp
-polyps reproduce sexually when colony grows to a certain size & conditions are right
Sexual reproduction & anisogamy
-recombination promotes genetic variation & increase capacity of populations to evolve in
response to environmental challenges
-meiosis produces haploid gametes
-transmit only half of its genetic material to each offspring
-growth rate is half that of asexually reproducing one