chapter 56 ecology Flashcards
Environmental Challenge
Ecology Study of how organisms relate to one another and to their environments Key elements of the environment Temperature Water Sunlight Soil
Homeostasis
Individual must maintain a steady-state internal environment regardless of external environment
Beetle is catching water to help live in a dry environment
Some are “conformers” – adopt temperature, salinity of their surroundings
Reponses can be short or long term
Short term
From a few minutes, to an individual’s lifetime
Variety of ways to cope
Long term
Natural selection can operate to make a population better adapted to the environment
Some have coping mechanisms:
Physiological responses Sweating, increased erythrocyte production, making “antifreeze” Morphological capabilities Endotherms have adaptations that minimize energy expenditure Thick fur coats during the winter Behavioral responses Moving from one habitat to another Maintain body temperature
Long term:
Natural selection leads to evolutionary adaptation to environmental conditions
Compare closely related species that live in different environments
Allen’s rule of reduced surface area:
Mammals from colder climates have shorter ears and limbs
Desert frogs: evolved a greatly reduced rate of water loss through skin
Populations
Populations
Groups of individuals of the same species in one place
3 characteristics of population ecology
Population range, area throughout which a population occurs
Pattern of spacing of individuals
How population changes in size through time
Range
Most species have limited geographic range
Devil’s hole pupfish lives in a single spring in southern Nevada
Polar bears are well adapted for the Arctic but you won’t find them in the tropics
Ranges change through time
Environment changes
Inhospitable habitat—colonize suitable, previously unoccupied areas
Humans have expanded ranges of coyotes, introduced starlings
Organisms have different dispersal mechanisms
Lizards colonized distant islands due to individuals or eggs floating or drifting on vegetation
Seeds of plants disperse in many ways
Individuals in populations exhibit different spacing patterns
Random spacing: individuals do not interact strongly with one another; not common in nature
Uniform spacing: behavioral interactions, resource competition
Clumped spacing: uneven distribution of resources; common in nature
Population Demography
Demography
Quantitative study of populations
How size changes through time
Whole population: increasing, decreasing, remaining constant
Population broken down into parts
Study birth and death rates of a specific age
Demography and Dynamics
Population growth can be influenced by the population’s sex ratio
Number of births directly related to number of females
Generation times: average interval between birth of an individual and birth of its offspring
Populations with short generations can increase in size more quickly than populations with long generations
Population Demography
Survivorship
Percent of an original population that survives to a given age
Survivorship curve
Express some aspects of age distribution
Life History
Natural selection favors traits that maximize the number of surviving offspring left in the next generation by an individual organism
2 factors affect this quantity
How long an individual lives
How many young it produces each year
In terms of natural selection, the number of offspring produced is not as important as how many of those offspring themselves survive to reproduce
Balance between number of offspring and size of offspring (and care to offspring)
Larger offspring (more care) have a greater chance of survival Producing many small offspring (less care) may result in very low survival rates
Age at first reproduction correlates with life span
Long-lived species delay reproduction
Advantage: juveniles gain experience before high cost of reproduction
Short-lived species reproduce early
Time is important; delay may mean no offspring
Environmental Limits to Population Growth
= (b – d) + (i – e)
r = rate of population increase; b = birth rate; d = death rate; i = immigration; e = emigration
When there are no limits on population growth, then:
ri is the intrinsic rate of natural increase for the population = innate capacity for growth
No growth limits on populationexponential growth model (J-shaped curve)
All populations eventually reach some limit imposed by a shortage
Carrying capacity: symbolized by K, is the maximum number of individuals that the environment can support
logistical growth (S-shaped curve)
Factors That Regulate Populations
Density-dependent
Factors that affect the population and depend on population size—affect birth rate and/or death rate—disease, buildup of toxic waste, predation, competition for resources
Density-independent
Other factors, such as natural disasters, affect populations regardless of size
Density-independent effects
Rate of growth of a population at any instant is limited by something unrelated to the size of the population
External environment aspects: cold winters, droughts, storms, volcanic eruptions
Populations display erratic growth patterns because of these events
Resource availability affects life history adaptations: limited resources vs. abundant resources
When resources are limited, the cost of reproduction is high
Selection will favor individuals that can compete and utilize resources efficiently
Can lower reproductive rates
K-selected populations: adapted to thrive when population is near its carrying capacity
Ex. Whooping cranes, whales, humans
