Midterm 1 Flashcards
1
Q
What is ecology?
A
The study of how organisms interact with each other and with the environment in which they live.
2
Q
What is evolution?
A
The study of how heritable traits change in populations over
successive generations
3
Q
Valuing biodiversity
A
•Market value
-US pharmaceutical research and development investments: >$50 billion annually
•Ecosystem services
•Tourism/recreation
•Cultural and intrinsic value
•Science/research
•Enjoyment
4
Q
Weather
A
current, short-term atmospheric conditions (e.g. temperature, rain, wind)
• “What should I wear today?”
•A big winter storm.
5
Q
Climate
A
average atmospheric conditions/patterns/cycles over many years/millennia
• “What clothes do I need to own for winter in Davis, California?”
•Typical patterns of flooding in a region
6
Q
latitude
A
•Latitude is described in degrees north or south of the equator
•Each degree north or south corresponds to ~69 miles of distance
7
Q
latitude
A
•towards th poles, more of the sun’s ray are absorbed because they must travel a longer distance through the atmosphere (north pole)
•At and near the equator, sunlight strikes Earth at a steep angel, delivering more heat and light per unit of area
•Towards the poles, the Sun’s rays strikes Earth at an oblique angel and are spread over a larger area, so that their energy is diffused (south pole)
8
Q
Hadley Cells
A
Hadley Cells are these patterns of atmospheric
circulation, with air rising near the equator (and raining), then descending as dry air at 30°N and 30°S
9
Q
Clouds
A
= moisture (rain)
10
Q
Dates are the same everywhere, but seasons are different in Northern and Southern Hemisphere
A
Equinox- March 20
Solstice- June 21
Equinox- September 22
Solstice- December 21
11
Q
Intertropical Convergence Zone (ITCZ) ≈ Thermal Equator
A
• The band of clouds/moisture/rain that shifts up and down periodically through the seasons
• The area with highest solar intensity
12
Q
Solar energy, Hadley cells, and climate
A
• Hadley cells: humid air rises (and forms clouds) near equator, drops as dry air about 30 degrees North and South.
• Average trend of humid tropical rainforest at equator, dry regions at 30°N and 30°S
• Because Earth’s axis is tilted, location of ITCZ/thermal equator moves (northernmost in June/July, southernmost in December/January).
• The E-W band around the Earth with the most rainfall (and clouds) shifts North or South at different times of year
13
Q
Rain Shadow
A
•Winds pick up moisture over the ocean
•on the windward side, air rises, cools, and releases moisture ae rain or snow, creating a wet climate
•On leeward side, dry air descends and warms, resulting in little rain and arid conditions
14
Q
atmosphere
A
-the air around the Earth
15
Q
greenhouse effect
A
Radiation from surface radiated back down to Earth
•Earth’s surface is warmed by incoming solar radiation and by back radiation from greenhouse gasses. this additional warming increases the outward radition from the surface.
•Greenhouse gasses in the atm absorb much of the surface reradition and radiate it back to the surface
16
Q
Greenhouse gas concentrations
A
-CO2
-N2O
CH4
CFC-12
CFC-11
HCF-22
HFC-134a
17
Q
CFC
A
any of a class of compounds of carbon, hydrogen, chlorine, and fluorine, typically gases used in refrigerants and aerosol propellants. They are harmful to the ozone layer in the earth’s atmosphere owing to the release of chlorine atoms on exposure to ultraviolet radiation.
18
Q
CFCs, ozone, and the chain reaction
A
- ozone is depleted to O2
-Effect of Montreal protocol
19
Q
CO2 is measured
A
This CO2 is measured directly by using ice cores – we can literally find ancient air and measure CO2 concentration.
20
Q
California Golbal heat record
A
• California is also generally warming – particularly in Southern California
• Relatively less snow is accumulating in the Sierra Nevada
mountains each Winter
•Of the 20 largest fires in California’s history (since
1932), 18 have occurred since 2000
21
Q
cryosphere
A
frozen water on Earth’s surface
22
Q
Decrease in global sea ice
A
•Sea ice has a typical annual pattern of increase and decrease.
•But the extent of sea ice has been declining over decades.
23
Q
Glaciers (+ ice sheets)
A
Glaciers- land based
Ice sheets- is the term for a large glacier (>50,000 km2)
24
Q
sea ice (+ ice shelves)
A
Iceberg- open ocean
Ice shelf- part of the Ocean
25
Cryosphere to Hydrosphere
Melting of ice sheets and other glaciers
26
hydrosphere
-liquid water on Earth’s surface
-sea levels are rising, the melting of the ice sheets and other glaciers
-Ocean absorbs heat, taking up any extra energy
-ocean warming up but slowly, causing tropical storms
-Ocean absorbs CO2 and acidities:
CO2 interacts with water (H2O) to create carbonic acid and free hydrogen ions.
Free hydrogen ions bind to carbonate to make hard-to-use
bicarbonate (rather than the carbonate that many organisms
need)
-As the ocean becomes more acidic effets marine life like corals, since they use CO2 to reinforce their shells
27
Representative Concentration Pathways (RCP)
trajectories for greenhouse gas concentrations
• 4 possible climate futures
• Time at which the global greenhouse gas emission
peaks and starts dropping
• RCP 2.6: global annual GHG emissions peak 2010-
2020, then decline significantly
• RCP 4.5: global annual GHG emissions peak 2040
• RCP 6.0: global annual GHG emissions peak 2080
• RCP 8.5: global annual GHG emissions continue at
current level
The number (2.6, 4.5, ….) refers to the strength of greenhouse effect (called “radiative forcing”) predicted in year 2100
Bigger number means more greenhouse effect (because of more greenhouse gases)
28
Levels of biological diversity
Genetic diversity: different in genotypes of individuals of the same species
Species diversity: different species occupying same habitat at same time
Other levels: different species assemblages in different habitats/ecosystems, species sharing evolutionary history, diversity in organisms’ ecological roles
29
Biodiversity
-Not ever where
-most in the tropical
30
Valuing biodiversity
• Market value: make money of plants
•Ecosystem services: bee pollinating
• tourism/recreation: open money to go into parks
• cultural and intrinsic value: a part of us
•science research: discover, know things
• enjoyment: positive impacts on people mental health
31
Quantifying biodiversity
Diversity Index- D
Species richness= total # species in habitat
Species evenness= relative abundance of each species
𝐷 = (𝑝1^−𝑝1)(𝑝2^−𝑝2) (𝑝3^−𝑝3)…(𝑝𝑛^−𝑝𝑛)
p is the proportion of individuals of that species
32
If the proportions were the same, but there were 200 frogs, how would D change?
Nothing would change, it's all about propotion
33
Quantifying biodiversity count
In most cases, you cannot directly count every organism
Instead, you may use quadrats or point counts, and then
extrapolate from this sample to the whole group
34
Rarefaction curves
Instead of diversity as a function of area, we can look at
diversity as a function of the # individuals sampled
plots of the number of individuals on the x-axis against the number of species on the y-axis.
35
Diversity curves and D
A higher D value = steeper curve
36
Vicariance
The geographic separation of a species into separate populations through some sort of physical barrier
• continents were one Pangea)
• plate tectonics: broke Pangea into continents
• land bridge
• people building roads
37
Most living tissues
•70% water by weight
•Ions and small molecules
• macromolecules
38
Every living organism contains about these some proportions by weight of the four kinds of macromolecules
• Proteins: are chains of amino acids
- 20 amino acids
-building blocks of: Carbon, Nitrogen, Hydrogen, Oxygen
• nucleic acids: DNA and RNA
-Nucleic acids include RNA (ribonucleic acid) as well as DNA (deoxyribonucleic acid). Both types of nucleic acids contain
the elements carbon, hydrogen, oxygen, nitrogen, and phosphorus.
• carbohydrates (polysacchorides): Glucose is C6 H12 O6
- starch and glycogen
• Lipids
39
Earth’s atmosphere
The atmosphere contains gaseous forms of carbon and nitrogen, but these are not easy to convert to more useable forms.
40
Carbon and nitrogen
Carbon and nitrogen have to be “fixed” to become useful to most organisms. This kind of fixation was limited to
prokaryotes (bacteria and archaeons).
41
Carbon fixation
Carbon fixation is storing the atmospheric carbon as a
carbohydrate, typically as glucose
Only bacteria could do this originally, but green plants gained
this ability through a symbiosis with a cyanobacterium. A
cyanobacterial symbiont became the chloroplast organelle
42
Nitrogen-fixation
Nitrogen-fixation also occurs in bacteria and some archaeons. Gaseous nitrogen is comprised of two molecules of nitrogen with a triple bond between them. This triple bond is very hard to break and requires the enzyme nitrogenase
The product of nitrogen fixation is ammonia. In this form, nitrogen is available to many other organisms
43
Photosynthesis
Photosynthesis occurs when atmospheric carbon (CO2) is
”fixed.” Fixation is storing the carbon as a carbohydrate, typically glucose
44
Photosynthesis requires
•A carbon source
•An electron donor
•Light energy (photons) and a pigment to harvest the energy
•Bacteria use bacteriochlorophyll, plants have other pigments.
45
WHEN water is used as the electron donor:
6CO2 + 12H2O + photons → C6 H12O 6 + 6O2 + 6H2O
carbon dioxide + water + light energy → carbohydrate + oxygen + water
Oxygen is released into the atmosphere.
This is oxygenic photosynthesis where carbon is fixed.
Photosynthesis that's not oxygenic, but also Photosynthesis when oxygen is released
46
Autotrophs
•Autotrophs live exclusively on inorganic sources of carbon, nitrogen, and other essential resources.
• There are chemoautotrophs and photoautotrophs. photoautotrophs which use sunlight as an energy source for metabolism and growth.
6CO2 + 12H2O + photons → C6 H12O 6 + 6O2 + 6H2O
carbon dioxide + water + light energy → carbohydrate + oxygen + water
47
How is the light energy for photosynthesis harvested?
Plants have 2 major body divisions: the root and the
shoot.
Light is harvested in the shoot using pigments.
48
Shoot system
The shoot system consists of stems and leaves, in which photosynthesis takes place
49
Root system
The root system anchors the plant and provides water and nutrients for the shoot system
50
Light exists in different wavelengths within the electromagnetic spectrum
Pigments absorb different wavelengths
• shorter wavelengths are more energetic
• longer wavelength are less energetic
• high wavelength = lots of light absorbed
• each wavelength have peak absorption, have two peaks
•
51
Light can be absorbed or reflected.
The color of a plant is what it's reflecting
52
What kinds of pigments exist?
• Chlorophyll a: All plants (absorbs at 350-430, 600-700nm)
• Chlorophyll b: land plants + green algae, (420-470, 580-630nm)
• Chlorophyll c: dinoflagellates, diatoms, brown algae (400-440, 590-610 -minor)
• Xanthophyll (fucoxanthin): diatoms, brown algae (400-500nm)
• Phycocyanin: cyanobacteria (500-650nm)
• Phycoerythrin: red algae (450-550nm)
What every it's mim is, is what its reflects
53
Trade-off
the relationship between the benefits of a trait in one
context and its costs in another context
Ex: Why might Anacharis have 3 pigments?
- making 3 pigments allows the absorption of more pigments. However reflecting these 3 payments spend more energy making these
Ex: Why might two organisms living in the same place have different pigments?
- so you are not in competition with each other one could live in light and other in shadow.
54
Principle of allocation
all life functions cannot be simultaneously maximized
55
Autotrophs
Autotrophs live exclusively on inorganic sources of carbon, nitrogen, and other essential resources.
• shoots collects photosynthesis
• CO2 entire and O2 and H2O exit the leaves through pores on the leaf surface called stomata
56
Stomata
the downside of opening stomata, plants could dry out
- under leaf to not dry out in the sun
- H2O enter through the roots
57
There is variation in exactly how and where photosynthesis takes place.
In 85% of the plants, the carbon from CO2 is accepted by a 5-carbon structure called RuBP.
CO2 is fixed when the enzyme rubisco adds one carbon to RuBP to make a 6-carbon compound.
- mesophyll cells have rubisco and fix CO2 to RuBR to form 3PG
• C3 plant
•C4 plant
•CAM plant
58
C3 plants
This 6-carbon compound quickly breaks into two 3-carbon compounds (3PG, so they are called C3 plants) that result in glucose production via the Calvin cycle.
All this takes place in the mid-leaf cells called
mesophylls.
59
C3 plants stomata
Stomata: the more open they are, the more CO2 can enter, but the more water is lost (a trade-off). Most stomata open and close via guard cells, but this takes energy.
The enzyme rubisco binds CO2, but it also binds oxygen, so stomata stay open a long time to collect C02
Binding oxygen results in production of a 2-carbon
compound that has to be modified to enter the Calvin Cycle—the cost of modification reduces net carbon fixed by 25%. This is photorespiration. Fixed only get 75%
60
C4 Plant
In about 8000 plants, mesophyll cells have a new enzyme, PEP, that binds CO2; PEP has a low affinity for oxygen, so stomata don’t need to stay open as long and it works if stomata are partially closed.
PEP carboxylase catalyzes formation of a 4-carbon storage compound. The 4-C compound diffuses into the bundle sheath cells. There CO2 is released!!
The extra CO2 prevents oxygen binding. Rubisco catalyzes the fixation of CO2 to 5-C RuBP so there is a 6-C compound that quickly makes two 3-C compounds for glucose production. This all takes place in the sheath cells.
More ATP is spent in the process. Better at high temperature, low CO2, and in drought conditions.
Initial CO2 fixation is spatially separated from the carbon fixation that leads to glucose production
61
CAM plants
It is cooler at night, so stomata open then.
Photosynthesis requires light, so why do this—what is the trade-off?
-CO2 is fixed at night in mesophyll cells as a 4-carbon storage compound. It stored overnight in the cell vacuole.
-In the day, the 4-C compound moves to chloroplasts in the mesophyll cells. There CO2 is released!!
Rubisco catalyzes the fixation of CO2 to 5-C RuBP. The resulting 6-C compound quickly makes two 3-C compounds for glucose production.
The stomata are closed all day.
Initial CO2 fixation is temporally separated from the carbon fixation that leads to glucose production.
62
living organisms the major elements of all these are
carbon, hydrogen, oxygen, nitrogen, and phosphorus.
63
Carbon and nitrogen
Carbon and nitrogen are present in gaseous forms, but they require special enzymes to ”fix” them into biologically useful forms.
Bacteria and forms derived from bacteria, such as a chloroplasts in plants, do this.
64
plants need macronutrients
In addition to carbon, plants need macronutrients (e.g., nitrogen (N), phosphorus (P), potassium (K) and micronutrients (e.g., iron (Fe), Calcium (Ca), etc).
If a plant is short of a micronutrient, then the shoot grows poorly.
Where do plants get micronutrients and water? Roots
Nitrates and nitrites and phosphates are usually negative ions that are water soluble; plants absorb them with water.
K and Ca are positively charged ions where uptake is active.
65
Another way to increase nutrient collection by roots
1) Plants form symbiotic relationships with root-loving fungi called
ecto-mycorrhizae. The fungi increase the root foraging area and may even connect plants with their neighbors
2) The roots of leguminous plants form symbiotic relationships
with a bacteria called Rhizobium that fixes nitrogen as ammonia. Nitrogenase does not work in the presence of oxygen, so plants invest energy in binding the oxygen to protect the bacteria.
66
ecto-mycorrhizae trade off
Plant make CO2 to give sugar to the fungus
67
Rhizobium cost
Leguminous plants: protect bacteria
68
Organisms acquire nutrients through autotrophy or heterotrophy.
• Autotrophs live exclusively on inorganic sources of carbon, nitrogen, and other essential resources. There are chemoautotrophs and photoautotrophs.
• Heterotrophs use pre-formed organic molecules (those made by other organisms) to acquire carbon, nitrogen, energy, and other essential resources. They eat other organisms of all types.
• “Functional groups” of organisms share a mode of living such as heterotrophy, or carnivory
69
Heterotrophs
Heterotrophs can be herbivores, carnivores, omnivores or detritivores
Herbivores spend a lot of time feeding and may need a diverse diet to meet all nutritional needs.
Carnivores feed much less frequently
70
Heterotrophs: generalists & specialists
Heterotrophs may be generalists eating many different foods, like this locust,
Pro: more food choices
or specialists like this tobacco hornworm that feeds only on tobacco and its relatives.
Pro: not a lot of competition
Cost: detoxifying the poison
71
stresses
Stress on organisms can be abiotic e.g., heating, cooling, drying, excessive wetness, salt concentrations, acidity, etc.
We will look at temperature stress.
Stress on organisms can biotic: e.g., consumers, competitors, etc.
We will look at stress as a result of consumers (predators/herbivores)
72
abiotic stress:
Why does temperature matter?
Changes in temperature affect:
(1) the rates of biological reactions.
(2) the shapes of proteins, including the shapes of enzymes, so some processes may not work at extreme temperatures.
(3) the properties of biological membranes required for cell integrity
73
abiotic stress: temp matter?
Organisms cope at the cellular level:
Organisms cope at the cellular level:
1. Organisms can make heat shock proteins (hsp’s), also called chaperonins, to stabilize the structures of other proteins and prevent inappropriate binding.
Cost a lot to do this
Hsp’s are present in almost all life from bacteria to humans.
2. Organisms can produce several versions of enzymes, each suited to different temperatures.
74
Organisms have different thermal optima:
(1) some archaeons live in volcanic sulfur springs at 163 degrees Fahrenheit.
(2) Organisms have zones where they can regulate temperature, with and without spending energy.
•Within the thermoneutral zone, body temp is regulated by low energetic cost mechanisms, such as changes in blood flow to the skin and changes in posture
•Below the lower critical temp, the animal expends energy to produce metabolism heat
•Above the upper critical temp, the animal expends energy to lose heat by panting or sweating
75
Ectotherms
Ectotherms: body temperature determined primarily by external conditions.
•Outside temp
• behavior allows it to regulate temp ie. Hind underground for more heat. Uses less energy
• exposing darkly pigmented back to the sun increases heat gain by radiation
• pressing flat against tree reduces heat loss by conduction
•ectotherms rely on morphological and behavioral mechanisms of temp regulation
76
Endotherms
Endotherms: body temperature determined primarily by internal, metabolic rates.
• cost more in cold weather
• easy to stay at thermoneutral zone
•Endothermy is a high-benefit/high-cost strategy that works when resources (fuel for producing heat) are predictably abundant.
•Conduction is the direct transfer of heat when objects of different temp come into contact
•Warmer objects lose heat to cooler objects by radiation
•Evaporation of water from body surfaces or breathing passages cools he body
77
What can organisms do with shape?
Leaf morphology:
•Reflective leaves reduce radiation gain. Dark leaves increase radiation gain
Plant morphology:
•Arctic and high altitude
-Low growth form reduces loss to conduction
-Hugs ground to gain conduction from rock
-Leaves perpendicular to the sun’s rays to increase radiation gain
•Desert
-Open growth form results in high loss to conduction
-Open form has less conductive gain
- Leaves parallel to the sun’s rays to reduce radiation gain
78
What can animals do?
Endothermic:
•In rabbits, blood flow to ears with a large surface area allows heat exchange with the environment.
•Body shape conserves or releases heat—compare bunnies.
Ectotherms:
•Even ectotherms regulate blood flow to the skin; here iguanas increase heart rate to bring more blood to the skin to warm up.
•Behavioral regulation also occurs—e.g., spray water on yourself
79
Evaporative heat loss occurs through panting, sweating, or transpiration (cools leaves).
High heat of vaporization:
• sweating uses evaporation of water to cool the body
Cohesion:
•waters cohesive strength helps it flow from the roots to the leaves in a tree
• as water is lose through stomata, root constantly bring water up through the plant
80
For plants, water loss reduces photosynthetic rates.
• Plants can vary the number of stomata present by shedding leaves or making new leaves with fewer stomata.
• Some plants that live in extremely dry habitats (xeric habitats) have
stomata in internal pockets (crypts); hairs called trichomes reduce air flow to the pocket.
81
Can it be too cold?
Ice crystals inside cells destroy cell organelles and membranes.
In response:
• Intracellular water is moved to the extracellular space.
• Urea and glucose are added to cells to act as a natural antifreeze.
These frogs freeze solid and still survive; most organisms cannot do that.
There are some thermogenic plants like the eastern skunk cabbage
82
Stress due to the likelihood of being eaten is a biotic factor: Probability (p) of being eaten = p (detection) x p(capture) x p(consumption)
•detection
Probability (p) of being eaten = p (detection).
Reducing any of these factors increases survivorship (benefit), but adaptations are costly.
Costs:
(1) Need to stay in that habitat
(2) Reduced feeding time
Avoiding detection: camouflage or hiding
83
biotic factor:
p(capture)
Probability (p) of being eaten = p(capture)
Reducing any of these factors increases survivorship, but adaptations are costly.
Avoiding capture: schooling, herding, masting.
Costs are increased numbers of competitors
84
biotic factor:
consumption
Avoiding consumption:
(1) physical defenses
-Costs are in making the defense.
(2) Plants and slow-moving animals may be easily caught, so they often have chemical defenses.
-
85
Defenses may be constitutive (always present) or induced:
Induced
Induced animal defense example in the small aquatic arthropod ' Daphnia.
The invertebrate predators Chaoborus and Notonecta induced longer helmets, while the fish Lepomis induced shorter bodies but
had no effect on helmet length.
Longer tail spines (relative to body length) were induced by Notonecta and Lepomis.
The responses of D. retrocurva were influenced by algae concentration, with the more extreme responses occurring at a higher food concentration and higher lipid index.
86
Adaptation vs. Acclimation
•Adaptation: evolutionary change in genotype that maximizes performance
Inuit people have lived above arctic circle for 10,000+ years
Barrel-shaped body, short limbs, subcutaneous fat all over body incl. hands, shunt blood to extremities
•Acclimation: change in phenotype within an individual's lifetime to maximize performance (usually reversible)
World's greatest long-distance, col water swimmer Body optimized at 40% body fat (internal wet suit)
87
life history
The lifetime pattern of growth, reproduction, and survival for an
average individual.
88
life history strategy
The way in which individuals within and among species allocate
resources to growth, reproduction, and survival based on genetic
and environmental factors
89
Two very different patterns of investment in offspring:
• Few offspring, poor dispersal, lots of resources per offspring
• many offspring, broad dispersal, little investment per offspring
90
Principle of allocation
Principle of allocation: Tradeoffs exist and there is no way that all
life functions can be maximized simultaneously; there must be
compromises between competing demands.
Each of these life history questions deals with resource allocation.
Any answer to one question has consequences for allocation to other events in the life history
91
when to begin reproducing
•Reproduction diverts energy from growth.
•Size at first reproduction varies. Reproducing earlier generally means reproducing at a smaller body size. The sooner offspring are
made, the sooner they can make offspring, so there can be a advantage to reproducing early (compound interest argument).
•If delaying reproduction means you will make more offspring once you start reproducing, then delays can be advantageous, but there needs to be a high likelihood of living that long.
- however, you may die before this
92
reproducing size
•In some cases, male animals begin to reproduce early and remain
much smaller than females.
- the available of sperm is early so they reproduce early meaning less energy to grow
•Reproductive males are smaller than reproductive females in
spiders and Crepidula.
-competition to find a female to mate with
•Reproductive males are many times larger than females in
Northern elephant seals.
- high competition with other males. Protect females, have to fight
93
How many times in your life should you reproduce?
•Semelparous means you only reproduce once;
•iteroparous means you reproduce several times.
94
R-selected
Offspring: many small
- dispersed; limited parental care
Parental size: small body size
Life span: short life
Allocation pattern: Allocate to rapid growth
Reproductive timing: Early reproduction
Number of reproductive events: Semelparous (high effort)
Population Density: Environmental conditions keep the population at low density
Habitat: Unpredictable, variable, harsh or disturbed
Sources of mortality: Mortality is independent of other organisms and often catastrophi
95
K-selected
Offspring: Fewer large
-Not dispersed; more parental care
Parental size: Large body size
Life span: Longer life -
Allocation pattern: Allocate to slower growth, persistence, and defense
Reproductive timing: Delayed reproduction
Number of reproductive events: Iteroparous
Population Density: Environmental conditions allow populations of reach high density
Habitat: Predictable and favorable for growth and survival
Sources of mortality: Mortality is often caused by interactions with other organisms
96
Factors influencing population growth
Equations are just (technically precise) sentences.
The change in population depends on births, deaths, and migration
into and out of the environment
∆𝑁 = 𝐵 − 𝐷 + 𝐼 − 𝐸
• N = current population size ∆N = the change in population size
• B = number of births
• D = number of deaths
• I = number of immigrants
• E = number of emigrants
97
Exponential growth
Let’s ignore migration, then…
∆𝑁 = 𝐵 − 𝐷
• Births come from a birth rate (b) times the population size N
• Deaths come from a death rate (d) times N
∆𝑁 = 𝑏𝑁 − 𝑑𝑁
= 𝑏 − 𝑑 𝑁
= 𝑟𝑁
• We call r the intrinsic growth rate of a population. It incorporates
birth and death
Sentence version: the change in population size equals the
intrinsic growth rate times the current population size
98
Predicting population size: exponential growth
We can “solve” the previous equation to get a prediction for the ' ' population size at time t.
𝑁𝑡 = 𝑁0𝑒𝑟𝑡
Sentence version: The population at time t depends on the initial population size and grows/declines exponentially through time (r determines the exact rate)
Nt is population at time t (in whatever units), N0 is population at time 0
For a population with 500 individuals, with r = 0.25 (per year), what will the population be after 10 years?
500*e^(0.25*10) = 6091.2 ≈ 6091 individuals
99
Mark-recapture
In reality, N is usually unknown, so it’s simpler to rewrite as
𝑁 =(𝑛1 ∗ 𝑛2)/𝑀
(n1/N) = (M/n2)
n1: marked initially
N: estimated population size
M: marked recaptures
n2: total in second sample
100
Does exponential growth occur?
•Generally, we expect exponential growth when looking at small populations that are recovering or newly established at a location
• Some r-strategist species (like the variety of grasshoppers referred to as locusts) will have exponential growth combined with periods of rapid mortality
• decline: lost of habitat
• If a population is able to reach a large enough size, population growth will slow down and eventually stop
101
Density-independent controls
•Factors affecting population size that DO NOT depend on the number of organisms in the population, usually abiotic factors
- drought: weather
•Factors affecting population size that DO depend on the number of organisms in the population, usually biotic factors
-Density-dependent controls prevent a population from growing forever
- disease
- predation
- limited resources (e.g. Space)
102
Logistic growth: differential equation
(dN/dt) = rN [(K-N)/K]
Just one new term affectinggrowth rate (K-N)/K
Sentence version: the change in population size equals the intrinsic growth rate times the current population size times a factor that shrinks as the population size approaches K.
When N is large, (K-N)≈0, so (K-N)/K ≈0 Growth slows to 0
When N is small, (K-N)≈K, so (K-N)/K ≈1 Growth is nearly exponential
103
Logistic growth: predicting population size
Nt= {K/1+[(K-N0)/N0]e^(-rt)]}
This term goes to 0 as t increases (so Nt goes to K). This happens faster when r is larger.
104
R-strategist species
r-strategist species tend to have a high intrinsic growth rate (r), but
density-independentfactors prevent populations from reaching their carrying capacity
105
K-strategist species
K-strategist species tend to have lower r and population size is often near carrying capacity K
