ch 8 ecology
Terms in this set (39)
spend 13 or 17 years underground as nymphs and then emerge from the ground in synchrony to mate.
Organisms differ in the number of times they reproduce before________
In almost all species, individuals eventually experience a decline in body condition followed by death (i.e., senescence).
Longevity (life expectancy):
the life span of an organism.
the number of offspring produced by an organism per reproductive episode.
the schedule of an organism's growth, development, reproduction, and survival; represents an allocation of limited time and resources to achieve maximum reproductive success.
the time and energy given to an offspring by its parents.
"Slow" life history
Long time to sexual maturity
Long life spans
Low numbers of offspring
High parental investment
Examples: elephants, oak trees
"Fast" life history
Short time to sexual maturity
Short life spans
High numbers of offspring
Little parental investment
Examples: fruit flies, weeds
J. Philip Grime
proposed that plant life history depends on stress, competition, and the frequency of disturbances.
Plants functioning at the extremes of these environmental axes could be categorized as
competitors increasing competition
stress tolerators increasing stress
funerals increasing disturbance
Stress tolerators are typically
small herbs with a long life span, slow growth, and a long time to sexual maturity.
Many stress tolerators rely on vegetative reproduction instead of producing costly seeds.
under less stressful they grow fast, achieve early sexual maturity, and devote little energy to seed production.
Ruderals (weeds such as Canada thistle)
grow fast and devote a high proportion of their energy to reproduction.
Principle of allocation:
the observation that when resources are devoted to one body structure, physiological function, or behavior, they cannot be allotted to another.
Natural selection will favor individuals that allocate their resources in a way that achieves maximum fitness.
Most organisms face a trade-off between
the number of offspring they can produce and the size of those offspring.
This indicates that selection favors a uniform offspring size.
Offspring number vs. parental care
Depends on environmental conditions, such as the number of daylight hours that parents have to find resources for their offspring.
Researchers can test for this trade-off by manipulating the number of offspring that a parent has.
Removal of eggs from a magpie's nest results in fewer total offspring.
Addition of eggs from the nest also results in fewer offspring because competition among chicks causes slower growth and higher mortality.
Parental care vs. parental survival
Kestrels lay on avg 5 eggs
Researchers added, removed, or did not change (control) the number of eggs in kestrel nests.
98% chicks in removal and control nests survived. Chicks in enlarged broods were malnourished and only 81% survived.
Threshold in which gains by increasing offspring are offset by increased adult mortality
Having more offspring can stimulate parents to hunt harder for food to feed their offspring.
This additional effort can affect the parent's fitness.
a growth pattern in which an individual does not grow any more once it initiates reproduction; occurs in many species of birds and mammals.
a growth pattern in which an individual continues to grow after it initiates reproduction; occurs in many species of plants, invertebrates, fishes, reptiles, and amphibians.
Organisms with a long life span should favor
determinate growth, which allows them to grow first and reproduce later.
Organisms with a short life span should favor
indeterminate growth, which allows them to quickly reproduce before death.
Delaying sexual maturity
allows an individual to grow large and produce more offspring per year once reproduction begins.
Comparing across many species (within taxonomic groups), the age of sexual maturity is positively associated with the
number of years an animal will survive after reaching maturity.
One can test the trade off of growth, age of maturity and lifespan. The Trinidadian guppy is common to the streams of Trinidad.
In high predation risk streams guppies have_______
In predator-free streams, guppies have________
Differences in life expectancies correlate with aspects of life history.
short life expectancies
long life expectancies.
an organism that has a life span of one year.
an organism that has a life span of more than one year.
are semelparous tropical plants that have few opportunities for seed germination.
Once a bamboo germinates, it spreads vegetatively for years.
Breeding is often synchronous over large areas, which may overwhelm seed predators.
are semelparous, arid plants that reproduce by growing a giant flowering stalk that produces a large number of seeds.
Stalk growth is so rapid that it must steal water and nutrients from the leaves; the plant dies soon after
are mostly iteroparous, but some varieties are semelparous.
Semelparous varieties live in regions prone to fire, which may favor a single, large reproduction effort before fires kill adults.
Iteroparous varieties live where there is less precipitation, but less chance of fire.
Differences in breeding patterns lead to tradeoffs in flower and fruit numbers, and in germination rates.
spend the first part of their life underground where they obtain nutrients from xylem tissue of plant roots.
Between the ages of 30 and 85, the rates of human metabolism, nerve conduction, blood circulation, and breathing capacity decrease up to 65%.
Over time, the function of the immune system also declines, leading to higher death rates.
Why does senescence exist?
Senescence is an inevitable consequence of natural wear and tear.
Senescence might reflect the accumulation of molecular defects that fail to be repaired (e.g., from ultraviolet radiation).
In Michigan, water fleas (Daphnia) enter diapause in mid-September when the photoperiod declines to less than 12 hours of sunlight.
Related species in Alaska enter diapause in August when the photoperiod declines to less than 20 hours of sunlight.
Photoperiod sensitivity have been adjusted by natural selection so the organismal response matches environmental conditions..
the amount of light that occurs each day; provides a cue for many events in the life histories of virtually all organisms.
Predation can affect
many life history traits (e.g., time to and size at hatching, metamorphosis, and sexual maturity).
Small changes in temperature can have substantial impacts on an organism's
The increase in global temperature has changed the
breeding times of many animals and plants.
Researchers recently recorded the flowering times of these species today.
They found that local temperatures had increased by 2.4°C and flowering time occured 7 days earlier.
Problems can arise when a species depends on the environment to provide the necessary resources with an altered breeding season.
The pied flycatcher breeds in Europe each spring.
In 1980, the date of egg hatching began a few days before the peak of caterpillar abundance, which is prey for the flycatchers.
Over the next two decades, spring temperatures warmed and peak caterpillar abundance shifted to two weeks earlier.
The pied flycatcher retained its normal breeding time.
As a result, newly hatched chicks no longer have their major source of food and flycatcher populations have declined by 90%.
In addition to global warming, human activities can impose strong selection and have substantial impacts on organisms' life histories.
Commercial fisheries impose selection pressure on fish size by harvesting only the largest individuals.
Between the 1930's and 1970's, the average age at maturity of northeast Arctic cod decreased from 9-11 years to 7-9 years.
This shift is likely associated with changes in fecundity and longevity.
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