Midterm Flashcards
1
Q
Ecology
A
Scientific study of interactions between organisms and their environment
2
Q
Controlled experiment
A
Experimental groups are compared with a control group that lacks the factor being tested.
No control= no real experiment
3
Q
Standard error
A
Graphs with smaller standard error are more accurate. You can make a standard error smaller by replicating.
4
Q
Case study: factors affecting amphibian declines
A
- habitat loss
- pathogens
- climate change
- Ribeiroia trematoe flatworms
5
Q
Scientific Method
A
- Make observations and ask questions (pattern)
- Use previous knowledge or intuition to develop hypothesis (process)
- Evaluate hypothesis by experimentation, observational studies, or quantitative models
- Use the results to modify the hypotheses, pose new questions, or draw conclusions about the natural world
6
Q
Experimental design
A
- Replicate- perform each treatment more than once on independent units
- Assign treatments at random
- Analyze results using statistical methods
7
Q
Observational field study
A
2 groups and you sample them
Ex) one’s healthy and one’s deformed
8
Q
Controlled experiment
A
Able to control the variables
Ex) tadpoles and parasite Ribeiroia in the lab
9
Q
Field experiment
A
Cages
Ex) ponds with pesticides vs. No pesticides; cages for pesticides
10
Q
Spatial scales
A
Small: soil micrrorganisms
Large: atmospheric pollutants
11
Q
Temporal scales
A
Short: leaf response to sunlight
Long: how species change over geologic time
12
Q
Levels of Biological Organization
A
Individual Population Community (diff species) Ecosystem (abiotic and biotic) Landscape Biosphere
13
Q
Population
A
Group of individuals of a species that are living and interacting in a particular area
14
Q
Community
A
Association of populations of different species in the same area
15
Q
Ecosystem
A
Community of organisms (biotic) plus the physical environment (abiotic)
16
Q
Landscapes
A
Heterogenous areas, including multiple ecosystems that are connected
17
Q
Biosphere
A
All living organisms on earth plus the environments in which they live
18
Q
Evolution
A
- Change in genetic characteristics of a population over time
- Descent with modification- organisms gradually accumulate differences from their ancestors
19
Q
Adaptation
A
A characteristic that improves survival or reproduction
20
Q
Natural selection
A
Individuals with certain adaptations tend to survive and reproduce at a higher rate than other individuals
21
Q
If the adaptation is heritable…
A
The frequency of the characteristic may increase in a population over time.
Ie) superbug evolution
22
Q
Ecosystem processes
A
- energy moves through ecosystems in a single direction only- it cannot be recycled
- nutrients are continuously recycled from the physical environment to organisms and back again- that is the nutrient cycle.
23
Q
Producers
A
Capture energy from an external source (eg. The sun) and use it to produce food
24
Q
Net primary productivity (NPP)
A
(Accumulation of energy)
-energy captured by producers, minus the amount lost as heat in cellular respiration
25
Consumers
Get energy by eating other organisms or their remains
26
What is causing changes in salmon catch?
- threats to streams
| - changes in the oceans
27
Threats to streams
Damming, pollution, and overfishing
28
Changes in the ocean
- climatic variation in the North Pacific
- periods of high salmon production in Alaska= periods of low production in Oregon and Washington
- correlation between salmon production shifts and sea surface temperatures
29
Pacific Decadal Oscillation (PDO)
Associated with 20 to 30 year cycles of warm and cool temperatures in the North Pacific
30
Weather
Current conditions- temperature, precipitation, humidity, cloud cover
31
Climate
Long-term description of weather, based on averages and variation measured over decades
-characterized by average conditions, but extreme conditions are also important
32
Mediterranean-type climate
Precipitation is concentrated in winter
33
Grassland precipitation
Spread evenly throughout the year
34
Conduction
Kinetic energy is transferred by molecules in direct contact with one another
35
Convection
Energy transfer by movements of air or water currents
36
Sensible heat flux
Energy transfer from warm air immediately above the surface to the cooler atmosphere by convection and conduction
37
Greenhouse gasses
Absorb and reradiate the infrared radiation emitted by Earth
- water vapor (H2O)
- carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
38
Consequences of greenhouse gases
-without any greenhouse gasses in the atmosphere it would be 33 degrees colder. They have a pretty strong impact
39
Solar radiation
- poles the sun's rays are spread over a larger area and take a longer path through the atmosphere
- near the equator, the sun's rays strike earth's surface perpendicularly
40
Surface heating and uplift
- warm air is less dense than cool air, so the air above the warm surface rises
- as the warm air rises, it expands and cools
- eventually the air cools enough to form clouds
41
Where do clouds usually form?
Troposphere and stratosphere.
| Also near the trophics leading to a low pressure zone
42
Where do deserts usually occur?
At areas of very low precipitation at high pressures
43
Atmospheric Circulation
- warmee air moves from the equator north and south
- air from the poles moves back down towards the surface
- ferrell cell fluctuates the most. Is the temperate zone
44
Polar cell, Ferrell cell, and the Hadley cell result in which 3 major climatic zones?
Occurs in each hemisphere:
1. Tropical
2. Temperate
3. Polar
45
Prevailing winds
Areas of high and low pressure created by the circulation cells resulting in air movements
46
The Coriolis Effect
Winds appear to be deflected due to the rotation of the Earth
47
Global Wind Patterns
- prevailing winds change depending on the time of year
| - wind tends to blow from areas of low pressure to areas of high pressure
48
Ocean Circulation
- ocean currents are largely determined by prevailing winds
| - wind produces drag on the surface of the water, and over time creates directions
49
Polar Downwelling
- Where warm tropical surface currents reach polar areas: the water cools, ice forms, the water becomes more saline and more dense and sinks (downwelling).
- The downwelling water mass moves back towards the equator, carrying cold polar water
50
Coastal upwelling
- brings nutrients up into the zone with life feeding lots of small organisms
- most zones of water remain pretty much unmixed
51
Coastal upwelling
- where deep ocean water rises to the surface
- occurs where prevailing winds blow parallel to a coastline
- surface water flows away from the coast and deeper, colder ocean water rises up to replace it
52
Large-scale atmospheric and oceanic circulation patterns establish global patterns of temperature and precipitation
- average annual temperatures become progressively cooler from the equator toward the poles
- this pattern is altered by ocean currents, continental topography, and the distribution of land and water masses
53
Do temperatures fluctuate more over land or water?
More over land
54
Precipitation patterns associated with atmospheric circulation cells are modified by what?
Mountain ranges, semipermanent high- and low-pressure zones
55
Rain shadow effect
Moist on one mountain side. Arid on the other. Can also see major wind pattern differences on either side.
56
Evapotranspiration
Water loss through transpiration by plants, plus evaporation from the soil.
-transfers energy (as latent heat) and water into the atmosphere, thereby affecting air temperature and moisture
57
Albedo
Capacity of a land surface to reflect solar radiation- is influenced by vegetation type, soils, and topography
-rates of evapotransporation greatly decline in deforested areas. Causing the local climate to get dryer and hotter
58
Seasonality
- temperate and polar zones have pronounced seasonal variation in solar radiation and temperature
- difference in seasonal solar radiation increases from the tropics toward the poles, and results in varying day lengths
- seasonality influences biological activity and distributions of organisms
- aquatic environments also experience seasonal changes in temperature
59
Aquatic stratification
- affects nutrients and oxygen
- complete mixing (turnover) occurs in spring and fall
- water, depending on its temperature, changes density
60
El Nino
Are longer-scale climate variations that occur every 3 to 8 years and last about 18 months
61
La Nina
Events are stronger phases of the normal pattern, with high pressure off the coast of South America and low pressures in the western Pacific
62
Long-term Considerations
- earth's climate alternates between warm and cool cycles
- warmer periods are associated with higher concentrations of greenhouse gases
- earth is currently in a cool phase characterized by formation of glaciers, followed by warm periods with glacial melting
- these glacial-interglacial cycles occur at frequencies of about 100, 000 years
63
Milankovitch Cycles
The glacial-interglacial cycles have been explained by regular changes in the shape of Earth's orbit and the tilt of its axis
64
The chemical environment
Key chemical determinants of biological function:
- salinity
- acidity
- oxygen availability
65
Salnization
Soils in arid regions become saline when water is brought to the surface by plant roots or irrigation, and high rates of evapotranspiration result in salt build-up
66
Acidity
Ability of a solution to act as an acid: a compound that gives up protons (H+) to a solution
67
Alkalinity
Ability of a solution to act as a base: a compound that takes up H+ or gives up hydroxide ions (OH-)
68
What are biomes characterized by?
Leaf decidousness and succulence
69
Convergent evolution
- plants don't move around, so they're forced to adapt and make it work where they are
- so plants can be morphologically similar (function the same), but be taxinomically different
- immobility of plants make them vulnerable to selective pressures
70
Terrestrail biomes
- characterized by growth forms of the dominant plants, such as leaf decidousness or succulence
- similar biotic assemblages indicate similar responses to climatic forces in different locations
- plants are best for this classification
71
Tropical rainforest
- high biomass, high diversity: about 50% of Earth's species
- 11% of Earth's terrestrial vegetation cover
- no seasonal changes
- best tropical rainforests occur between 10 degrees N and S of the equator
72
Tropical deforestation
- disappearing due to logging and conversion to pasture and croplands
- about 50% of the tropical rainforest biome had been altered
- soils are nutrient poor
- nutirents are in the living material
- when the huge massive vegetation is removed and converted to farmland it makes it hotter and dryer
73
Tropical Seasonal Forests and Savannas
- wet and dry seasons
- shorter trees, deciduous in dry seasons, more grasses and shrubs
- less than 50% have been unaltered by human activity
- threats: human population growth, converted to cropland and pasture
74
Hot Deserts
- sparse vegetation and animal populations
- abundance may be low but species diversity cam be high
- 30 degrees N and S of the equator; exception being those formed by rain shadows
75
Temperate Grasslands
- maintained by frequent fires and large herbivores such as bison
- grasses grow more roots than stems and leaves, to cope with dry conditions
- most human impacted biome on the planet due to high soil fertility
- grasslands more continental
- shrublands and woodlands more coastal
76
Temperature Shrublands and Woodlands
- evergreen shrubs and trees
- Mediterranean-type climates: wet winters and hot, dry summers
- fire is common
- converted to crops and vineyards, but the soils are nutrient-poor
- shrublands in continental interiors occur in rain shadows and seasonally cold climates
77
Temperate Deciduous Forests
- species diversity lower than tropical rainforests, but still high
- more precipitation tends to occur when its warm
- fertile soils and climate make this biome good for agriculture
78
Temperate evergreen forests
- they receive high rainfall amounts and have mild winters
- lower diversity than tropical and decidous forest
- pine needles tend to be slightly acidic
- high acidity tends to increase leaching
- extensive clearing. Sometimes trees replaced with non-native species
79
Boreal Forest (Taiga)
- permafrost (soil that remains frozen year round) prevents drainage and results in saturated soils
- cold, wet conditions in boreal soils limit decomposition, so soils have high organic matter
- lakes lost once permafrost is gone because nothing to support the lake
- have not been as impacted by human activities though impacts are accelerating
80
Tundra
- widespread permafrost
- largest pristine areas on earth
- increased exploration and development of energy resources
- arctic warming at almost double the global average
- further N and S most severe impacts of climate change
81
Mountains (Elevation)
On mountains, temperature and precipitation change with elevation, resulting in zones similar to biones
82
Marine Biological Zones
- determined by ocean depth, light availability, and the stability of the bottom substrate
- aphotic: where the light doesn't penetrate
83
Coral reefs
- restricted to warm, shallow water
- complex habitat: a huge diversity of marine life
- rates of biomass production are some of the highest in the world
84
Human impacts on marine biological zones
- polluntants and nutrients via river
- commercial fishing
- greenhouse gas emissions
- increase in UV radiation due to stratospheric ozone loss
- excess nutrients algae growth
- coral bleaching
- acidification
85
Freshwater systems
Streams and rivers are lotic systems
- smallest streams are first order streams
- these converge to form second order streams
- large streams are 6th order streams or greater
86
Spatial zonation in streams
- distribuation of organisms reflect the energetic and environmental conditions experienced in progressively larger streams
- vast majority of life occurs where the nutrients are
- lakes are basically wide streams with less currents
87
Human impacts on freshwater habitats
- sewage and industrial wastes
- fertilizer runoff
- non-native species
- deforestation and erosion
- dams
88
Cryonics
Preservation of bodies by freezing
89
Physiological ecology
Study of interactions between organisms and the physical environments that influence their survival and persistence
90
Two options with environmental change?
Tolerance and avoidance
91
Climate envelope
Range of condition over which a species occurs
92
Stress
Environmental change results in decreased rates of physiological processess, lowering the potential for survival, growth, or reproduction
93
Acclimatization
Adjusting to stress through behavior or physiology (individuals)
94
Ecotypes
Populations with adaptations to unique environments
| -can eventually become separate species as populations diverge and become reproductively isolated
95
Latent heat transfer
Water absorbs heat as it changes from a liquid to a gas state
96
Stomata
Can control transpiration rates
97
Evaporative heat loss
Uncommon in animals
| Ex) sweating in humans
98
Ectotherms
Regulate body temperature through energy exchange with the external environment
99
Endotherms
Rely primarily on internal heat generation- mostly birds and mammals
100
Surface are to volume ratio
Affects the exchange of energy with the environment
101
Avoidance behavior
Includes seasonal migration
102
Tolerance to freezing
Involves minimizing damage associated with ice formation in cells
103
Thermoneutral zone
Range of environmental temperatures over which a constant basal metabolic rate can be maintained
104
Lower critical temperature
When heat loss is greater than metabolic production; body temperature drops and metabolic heat generation increases
105
Matric potential
energy associated with attractive forces on surfaces of large molecules inside cells or on surfaces of soil particles
106
Osmotic potential
Water flows from an area of high concentration to a region of low concentration
107
Hyperosmotic
More saline than environment
108
Isoosmotic
Same salinity as environment
109
Hypoosmotic
Less saline than environment
110
Evaporative water loss
Minimized by skin resistance, or by living in moist environments
111
Problems with freezing
- water forms needle-like ice crystals that can pierce cell membranes
- oxygen supply to tissues is restricted due to lack of breathing and circulation
- when ice forms, it pulls water from cells
112
Solutions to freezing
- freezing water is limited to the space outside the cells
- ice-nucleating proteins outside cells serve as sites of slow, controlled ice formation
- glucose and glycerol are made inside the cella to lower the freezing point
113
Holoparasites
Have no photosynthetic pigments and get energy from other plants
114
Hemiparasite
Is photosynthetic, but obtains nutrients, water, and some of its energy from the host plant
115
Photosynthesis (autotrophy)
Sunlight provides the energy to take up CO2 and synthesize organic compounds C-C bonds
116
Chemosynthesis (chemolithotrophy)
Energy from inorganic compounds is used to produce carbohydrates
117
Photosynthesis two major steps
1. Light reaction: light is harvested and used to split water and provide electrons to make ATP and NADPH
2. Dark reaction: CO2 is fixed in the Calvin cycle, and carbohydrates are synthesized
118
Light compensation point
Where CO2 uptake is balanced by CO2 loss by respiration
119
Saturation point
When photosynthesis no longer increases as light increases
120
Photorespiration is not advantages if
- low CO2
| - high temperatures
121
Crassulacean acid metabolism (CAM)
Minimizes water loss
122
Optimal foraging theory
Animals will maximize the amount of energy gained per unti time, energy, risk involved in finding food.
-assumes that evolution acts on behavior of animals to maximize their energy gain
123
Profitability of a food item (P)
Depends on how much energy (E) the animal gets from the food (net energy) relative to the amount of time (t) it spends finding and obtaining the food
124
Marginal value theorem
An animal should stay in a patch until the rate of energy gain has declined to match the average rate for the whole habitat (giving up time)
125
Critics to optimal foraging theory
- does not apply well to animals that feed on mobile prey
- for foragers, risk of exposure to their own predators is also important
- defensive behaviours of prey also influence the costs and benefits to foragers
126
Evolution
Change in allele frequencies (proportions) in a population overtime
127
Genes
Made of DNA and specify encode proteins
| -can have 2 or more forms called alleles
128
Genotype
Genetic makeup of an individual
129
Mutation
- change in DNA
| - produce new alleles
130
Recombination
- different combinations of alleles in offspring
| - produces different genotypes within a population
131
Phenotype
Observable characteristics of an individual
132
Phenotypic plasticity
Range of phenotypes produced by a genotype
133
Natural selection
Individuals with particular heritable traits survive and leave more offspring than others
134
Directional
Individuals with one extreme of a heritable phenotypic trait are favoured
135
Stabilizing
Individuals with an intermediate heritable phenotypic trait are favoured
136
Disruptive
Individuals at either extreme of a heritable phenotypic trait are favoured
137
Genetic drift
Low populations have chance events affecting which alleles passed to following generations
138
Gene flow
Alleles move between populations via movement of individuals or gametes
139
Adaptive evolution
Traits that confer advantages tend to increase in frequency over time
140
Natural selection does not result in a perfect match between organisms and their environments
1. Environments are constantly changing
| 2. Constraints on evolution
141
Species
Groups of organisms whose members have similar characteristics and can interbreed
142
Speciation
The process by which one species splits into two or more species
143
"Arms race"
Predators evolve adaptations to capture prey, and prey evolve adaptations to avoid being eaten
144
Coevolution
Reciprocal evolutionary change in interacting species
145
Human impacts on evolution
- extinction rate today is 100 to 1000 times higher than extinction rates seen in fossil records
- habitat fragmentation leaves isolated patches, which can affect evolutionary processes
146
life history
a record of events relating to its growth, development, reproduction, and survival.
- age and size at sexual maturity
- amount and timing of reproduction
- survival and mortality rates
147
Phenotypic plasticity
One genotype may produce different phenotypes under different environmental conditions
148
Polyphenism
a single genotype produces several distinct morphs
149
Isogamy
Gametes are equal in size ex) green alga)
150
Anisogamy
Gametes of different sizes
151
Complex life cycles
have at least two stages, with different body forms and that live in different habitats
152
Metamorphosis
Abrupt transition in form between the larval and juvenile stages.
153
Semelparous species
reproduce only once
154
Iteroparous species
can reproduce multiple times.
155
Competitive plants
with superior ability to acquire light, minerals, water, and space— have a selective advantage.
156
Stress-tolerant plants
with phenotypic plasticity, slow rates of water and nutrient use - not palatable to herbivores.
157
Ruderal plants
with short life span, rapid growth rates, heavy investment in seed production.
158
Stress
any abiotic factor that limits growth
159
disturbance
any process that destroys plant biomass
160
trade-offs
Organisms allocate limited energy or resources to one function at the expense of another
161
Provisioning eggs or embryos
yolk and protective coverings for eggs, nutrient-rich endosperm in plant seeds
162
Parental care
invest time and energy to feed and protect offspring.
163
Dormancy
State of suspended growth and development in which an organism can survive unfavorable conditions.
164
Niche shifts
should occur when the organism reaches a size at which conditions are more favorable in the adult habitat than in the larval habitat.
165
sequential hermaphroditism:
change in sex during the course of the life cycle
-Common in fish and invertebrates.
• The timing should take advantage of high reproductive potential of different sexes at different sizes.
166
Behavioral ecology
is the study of the ecological and evolutionary basis of animal behavior.
167
Proximate causes (immediate)
or how the behavior occurs.
168
Ultimate causes
why the behavior occurs; the evolutionary and historical reasons
169
Antipredator behaviors
include those that help prey avoid being seen, detect predators, prevent attack, or escape once attacked.
170
Perceived risk of predation
• can alter foraging patterns
171
Darwin proposed that the extravagant features of some males resulted from sexual selection
• Individuals with certain characteristics gain an advantage over others of the same sex solely with respect toto mating success.
172
Direct benefits: in some species, males provide females with
* gifts of food
* help in rearing young
* access to a territory with good nesting sites, food
173
Indirect benefits: other species, males provide nothing
females may receive indirect genetic benefits
174
The handicap hypothesis
* males support costly and unwieldy ornaments
| * Indication of vigorous individuals
175
The sexy son hypothesis
* female receives indirect genetic benefits through her sons
* attractive sons to females produce many grandchildren.
176
anisogamous species
females invest more to produce large eggs than male to produce sperm
177
Dilution effect
as the number of individuals in a group increases, the chance of being the one attacked by a predator decreases.
178
Flash effect
respond to a predator by scattering in different directions, making it difficult for the predator to select a target.
179
Costs of group living
* Food depletion
* More time spent moving between feeding sites.
* Subordinate members spend much time and energy on interacting with group members.
* Closer contact: parasites and diseases often spread more easily.
180
Population
Group of interacting individuals of the same species living in a particular area.
181
Abundance:
```
population size (# of individuals)
population density (# of individuals per unit area).
```
182
genet
single genetic individual. unique genetic makeup
183
ramet
members of a genet are independent physiologically
184
Dispersal limitation
can prevent species from reaching areas of suitable habitat
185
Geographic range
the entire geographic region over which a species is found.
186
Dispersion
Spatial arrangement of individuals within a population
187
Regular
individuals are evenly spaced. variance/ mean <1
188
Random
individuals scattered randomly. variance/mean ~1
189
Clumped
the most common pattern. Variance/mean >1
190
Relative population size
Number of individuals in one time period or place relative to the number in another.
191
I - Area-based counts
Used most often to estimate abundance of immobile organisms.
Quadrats: Sampling areas of specific size, such as 1 m2.
• Individuals are counted in several quadrats; the counts are averaged to estimate population size
192
II - Distance methods
Distances of individuals from a line or point are converted into estimates of abundance
Line transects:
Observer travels along line and counts individuals and their distance from the line.
193
III - Mark–recapture studies
Used for mobile organisms. A subset of individuals is captured and marked or tagged, then released. At a later date, individuals are captured again, and the ratio of marked to unmarked individuals is used to estimate population size.
194
ecological niche
physical and biological conditions that a species needs to grow, survive, and reproduce
195
niche model
predicts a species' distribution based on conditions at locations the species is known to occupy
196
Habitat rules
for each species described environmental conditions where it was most likely to be found
197
Sx = survival rate
Chance that an individual of age x will survive to age x + 1. Sx = Nx+1 / Nx
198
lx = survivorship
Proportion of individuals that survive from birth to age x. lx = Nx / N0
199
Fx = fecundity
Average number of offspring a female will have at age x.
200
Cohort life table
follows the fate of a group of individuals all born at the same time (a cohort).
201
Static life table
Survival and reproduction of individuals of different ages during a single time period (requires estimating age or some class interval).
202
Survivorship curves can vary
* Among populations of a species.
* Between males and females.
* Among cohorts that experience different environmental conditions
203
A population can be characterized by its age structure
the proportion of the population in each age class.
204
λ >1
population growth
205
dN/dt = rN
equation for exponential growth
206
λ = 1
population is stable
207
λ < 1
population decline
208
r=0
population stable
209
r > 1
population growth
210
r < 1
population decline
211
Assumptions of exponential growth
- no immigration or emigration
- no resource limitation
- no random mortality factors
- no age or size structure or stable age structure
- no genetic structure or constant genetic structure
- continuous growth with no time lags
212
Exponential growth
When individuals reproduce continuously, and generations can overlap.
213
Geometric growth
If a population reproduces in synchrony at discrete time periods
214
The population increases by a constant proportion
The number of individuals added is larger with each time period.
215
λ
geometric growth rate or per capita finite rate of increase. /generational
216
r
instant
217
Doubling time (td)
Number of years it will take a population to double
218
Net reproductive rate (R0)
Mean number of offspring produced by an individual during its lifetime
219
How do populations increase?
multiplication, not addition
220
Density-independent factors
Effects on birth and death rates are independent of the number of individuals in the population:
•Temperature and precipitation
•Catastrophes such as floods or hurricanes
221
Density-dependent factors
Birth, death, and dispersal rates change as the density of the population changes.
222
Population regulation
Density-dependent factors cause population to increase when density is low and decrease when density is high.
223
Density-independent factors
can have large effects on population size, but do not regulate population size
224
k
maximum carrying capacity
225
anything that affects r can
change the predicted k
226
logistic equation
incorporates limits to growth and shows how a population may stabilize at a maximum size, the carrying capacity.
227
Logistic or sigmoidal growth
Population increases rapidly, then stabilizes at the carrying capacity (maximum population size that can be supported indefinitely by the environment)
228
Ecological footprint
Total area of productive ecosystems required to support a population
229
λ < 1
r < 0
230
λ = 1
r = 0
231
λ > 1
r > 0
232
Population dynamics
The ways in which populations change in abundance over time.
233
four main patterns of growth
exponential growth, logistic growth, fluctuations, and regular cycles.
234
Exponential Growth
* Population increases by a constant proportion at each point in time.
* When conditions are favorable, a population can increase exponentially for a limited time.
235
Logistic Growth
Some populations reach a stable size (equilibrium) that changes little over time.
These populations first increase, then fluctuate by a small amount around the carrying capacity(‘K’, birth = death rate
236
Population Fluctuation
In all populations, numbers rise and fall over time.
| For K to be constant, birth rates and death rates must be constant over time at any given density.
237
Population Cycles
Some populations have alternating periods of high and low abundance at regular intervals.
Factors that drive population cycles may vary from place to place, and with different species.
238
Delayed density dependence
Delays in the effect that density has on population size.
239
Chance events
—genetic, demographic, and environmental events
—can play a role the extinction
Small populations, because of the “laws of probability”, are at greater risk.
240
Genetic drift
-chance events influence which alleles are passed on to the next generation.
Allele frequencies can change at random from one generation to the next:
- reduced genetic variation
- increased frequency of harmful alleles
241
Inbreeding
tends to increase the frequency of homozygotes:
•Individuals can have two copies of a harmful allele.
•Reproductive success is reduced.
242
Demographic stochasticity
chance events affect survival and reproduction of individuals.
243
Allee effects
At low densities, individuals have difficulty finding mates •growth rate decreases as population density decreases.
•Allee effects can reduce small population size even further
244
Environmental stochasticity
—change in average birth or death rates from year to year because of random changes in environmental conditions.
245
demographic stochasticity
—birth and death rates are constant, but the actual fates of individuals differ
246
Isolation by distance
travel distance is long and risky
247
patch size
small patches are hard to find and have high extinction rates
248
metapopulation
sets of spatially isolate populations, linked by dispersal
