Biology Unit 4 Ecology

What is Ecology?

• study of how organisms interact with their environment

Environment includes:

• abiotic: physical rather than biological; not derived from living organisms

• biotic: relates to living things; and their ecological relations

What is ecology used to understand?

• distribution and abundance of organisms

What are the Levels of Ecological Study?

1. Organisms

2. Populations

3. Communities

4. Ecosystems

5. Global

What is Organismal Ecology?

• explores the morphological, physiological, and behavioral adaptations allowing individuals to live in a particular area

Organismal Ecology Example

• Ex. Lizards are ectotherms, their body temps match the environment, can adapt to changes in temp in environment

Conclusion: thermoregulation is flexible in lizards as they can adjust time spent in different light in environments, to compensate for warmer temps

What do Organismal Ecologists measure?

how individuals interact with their physical surroundings and with other organisms in their habitat

What is Population Ecology?

• a group of individuals of the same species that live in the same area, at same time and interact

Population Ecology Example

• Ex. Locusts, which shift between:

• solitarious phase (avoid other locusts, is green, shy)

AND

• gregarious phase (social, bright, migrate in groups)

Conclusion: changes in weather affects reproduction of insect, causing ‘boom and bust’ periods that impact humans

What do Population Ecologists measure?

how the number of individuals in a population gradually change

What is Community Ecology?

• a biological community consisting of different populations of species that interact with one another in a particular area

(many species together)

Community Ecology Example

• Ex. Whitebark pine live at high elevations and multiple species rely on it, pinecones rely on Clark’s nutcracker to disperse and store seeds

• Conclusion: Species that rely on each other are found together, and losing one might disrupt the system

What do Community Ecologists study?

the nature and consequences of interactions among species

• ask questions about biotic interactions: responses to predation, parasitism and competition

• And abiotic interactions like responses to fire, floods, etc.

What is Ecosystem Ecology?

an ecosystem consists of all organisms in a particular region (community), along with nonliving components

• Ecosystem= biotic component + abiotic component

Ecosystem Ecology Example

Ex. Nitrogen is limiting and puts constraints on life. Increases or decreases in nitrogen change species composition and abundance of plants.

Conclusion: excess nitrogen input into ecosystems change complex interactions, affecting ecosystem health and abundance of certain species

What do Ecosystem Ecologists study?

• how nutrients and energy move among organisms and between surrounding, air, soil, and water

What is Global Ecology?

encompassed by biosphere; thin zone surrounding Earth where all life exists

• combo of all ecosystems and their interactions

Global Ecology Example

Ex. NPP (Net Primary Productivity) is how much CO₂ vegetation absorbs during photosynthesis minus how much CO₂ plants release during respiration

• important for understanding Earth’s global carbon cycle

Conclusion: NPP fluctuates over the season, has North/South patterns, varies year to year

What do Global Ecologists study?

focus on effects of human impacts on biosphere

Biogeography

study of how organisms are distributed geographically

• interactions with the abiotic and biotic environments affect where a particular species live

• Ex. Location of Lodgepole pine (left) vs Location of Jack pine (right)

What are Abiotic Factors?

Abiotic factors that limit ranges:

• Temperature

• Wind

• Water (availability)

• Light

• Salinity

• pH

What are Biotic Factors?

• distribution of species is limited by living factors, or interactions with other organisms

• Competition, Mutualism, Parasitism affect species distribution

Why is Earth’s history also a component in Ecology?

• continental drift has gradually changed the Earth’s oceans and landforms

As a result:

• climate has changed

• seas have risen and fallen

• glaciers have formed and receded

Example of change in Earth’s History

• the land bridge between North and South America formed 15-3 mya

Effects: 

• land species could disperse between continents

• however marine species were faced with a barrier between Pacific Ocean and the Caribbean Sea

Why is temperature important in species distribution?

• high and low temps explain species distribution

• a species becomes adapted to a range of temps and if exceeded, they move or die

How does water affect species distribution?

• water performs vital functions in all organisms

• species are adapted to a range of water conditions, and if exceeded, move or die

What is the difference between Climate and Weather?

• Climate is the prevailing long-term weather conditions found in an area

• Weather consists of the specific short-term atmospheric conditions of temperature, precipitation, sunlight, and wind

Why is it warmer at the Equator?

• At the equator, sunlight strikes the Earth at an angle allowing the maximal amount of solar radiation

• warmer areas receive more sunlight per unit area

• sunlight arrives at lower angles at the poles, minimizing energy and heat (30 N is moderate sunlight and 60 N, lowest amount)

Why is it wetter at the Equator?

• areas along the equator receive the most moisture whereas, area 30 N and 30 S latitude are drier

The Hadley Cell causes this to occur

Explain how the Hadley Cell works

• air heated at the equator expands and rises, warm air holds moisture

• as air rises it cools, holding less water, and precipitation occurs

• as more air is heated along equator, the cooler, “older” air above Earth’s surface is pushed toward poles

• as air cools, its density increases and it begins to sink

• as it sinks, it absorbs solar radiation from Earth’s surface and warms, gaining water-holding capacity

• warm air returns to surface at 30 N and 30 S, resulting in low precipitation (desert)

Explain the Coriolis Effect

• air within a cell does not move in a straight north-south direction

Coriolis Effect causes air to be deflected in a clockwise pattern around the globe in the Northern Hemisphere

• accounts for differences in directions of winds and ocean currents at different latitudes (water is cold in beach at CA)

What Causes Seasonality in Weather?

• Seasons: annual fluctuations in temps, precipitation, or both

• Seasons are caused by Earth’s 23.5 degree tilt on axis

• In December, the Southern Hemisphere is tilted towards the Sun, receiving the largest amount of solar radiation

• In March and September, the equator faces the Sun directly, tropics receive more solar radiation

Explain this model

How do Mountains and Oceans affect Climate? Rain shadow

• from the west side of the mountain, moisture-laden air blows onshore from Pacific Ocean

• then, air rises over mountains and cools; rain falls

• on the east side, dry air creates desert conditions (in rain shadow)

• major deserts formed like this (Great Basin Desert)

What Regional Effects do Mountains and Oceans have on Climate?

• oceans can influence temp because water has a high capacity for storing energy compared to land

• water absorbs atmospheric heat in summer and releases it during winter

• coastal areas (near oceans) have more moderate climates than inland areas (far from oceans)

• known as Maritime effect; where proximity to oceans influence a region’s climate

What are Gyres?

Gyres are massive ocean current cycles that transport warm water from equator to colder latitudes, and cold water toward tropics (regulates climate and influences ecosystem in different regions)

Coriolis effect causes:

• clockwise gyres in Northern Hemisphere and counterclockwise in Southern Hemisphere

What are Biomes?

regions characterized by distinct abiotic characters and dominant vegetation types

Depends on:

• Temperature defines range of species

• Moisture is required for life; organisms lose water to evaporation/transpiration

• Sunlight needed for photosynthesis

• Wind modifies effects of temperature and moisture

Natural Biomes

determined by:

• average annual temp and precipitation

• annual variation in temp and precipitation

What is NPP?

• NPP is the total amount of biomass produced by carbon fixed per year minus the amount of fixed carbon utilized during cellular respiration

• NPP refers to total mass of primary producers

• Biomass refers to the total mass of organisms

NPP in Nature Biomes

• NPP represents organic matter that is available as food for all organisms

• In terrestrial environ., NPP is estimated by measuring aboveground biomass

• On land, photosynthesis and plant growth are maximized when temps are warm and conditions wet

Arctic Tundra Biome

Description:

• in arctic regions of Northern Hemisphere

• low productivity, low species diversity, and low aboveground biomass

• soil can be permafrost

Vegetation:

• ground covered by low plants (lichens, woody shrubs), no trees

• little animal diversity, higher insect abundance (swarms of biting flies)

• short growing seasons

Avg. Precipitation and Temp:

• low precipitation and below freezing temps (Alaska)

• high annual temp variation

Boreal Forest Biome (Taiga)

Description:

• present across Canada, Alaska, Russia, and Northern Europe

• low prod. and low species diversity

•  dominated by cold-tolerant conifers (pines, spruce, fir, and larch trees)

• high aboveground biomass, many slow-growing species are long lived

• low structural diversity, moisture sufficient for tree growth

Avg. Precipitation and Temp:

• very cold winters and cool summers, temp variation extreme

• annual precip. low as cold temps minimize evaporation

Temperate Forest Biome

Description:

• in North America, Europe, and Eastern Asia

• moderate prod. and diversity because mean temps (below freezing) do not support photosynthesis year-round

Vegetation:

• dominated by deciduous trees (leafless in winter, grow new leaves in spring and summer)

• needle-leaved evergreens common

Avg. Precipitation and Temp:

• compared with grassland climates, precipitation is moderately high and constant throughout year

• temperature mean and variation is moderate

Temperate Grassland Biome

Description: 

• grasslands soils are more fertile, but productivity is lower in forests

Vegetation:

• grasses dominate as conditions are too dry for tree growth (can cause fires)

• extremely dense plant life both aboveground and belowground (roots)

• plant growth occurs when moisture and warmth are adequate

• Avg.  Precipitation and Temp:

• seasonal temp and rainfall are moderate

Subtropical Dessert Biome

Description:

• present at 30 latitude North and South

• has extreme temps, low moisture, and very low productivity

Vegetation:

• has cacti, leaves modified as pines (no leaves), or leaves with a thick, waxy coating (reduces water loss)

• slow growth year-round, or occurs during rainfall

Avg. Precipitation and Temp:

• very low precipitation

• mean monthly temps high, greater variation than in tropical wet climates

Tropical Wet Forest Biome (Tropical Rainforest)

Description:

• present in equatorial regions

• favorable year-round growing conditions produces high aboveground biomass, high species diversity, and high productivity

Vegetation:

• high NPP (more species diversity)

• plants have broad leaves, are evergreen, and diverse in size and growth

• high structural diversity (tall and short trees, vines, shrubs), presents wide array of habitats for animals

Avg. Precipitation and Temp:

• highest avg. temp, almost no seasonal variation in temp

• highest annual rainfall

Imagine you are in a Biome that exists at 30 degrees South and has very low precipitation. The plants you find are modified with no leaves. What Biome is this?

Desert

Imagine you are in Siberia and the forest has low diversity and is dominated by coniferous trees. What biome is this?

Boreal Forest

How does Water Depth affect the distribution and abundance of organisms in Aquatic Biomes?

• water absorbs and scatters light, the amount and type of wavelengths available to organisms change as water depth increases

• turbidity (cloudiness) of water is an important determinant of light penetration

• light has a major influence on NPP

Define the six zones in Ocean habitats

Intertidal Zone: the area where the ocean meets the land between high and low tides

Neritic Zone: the region of shallow water above continental shelf where light penetrates to sea floor

Benthic Zone: region at lowest body of water (lake, ocean)

Oceanic Zone: vast area of ocean beyond continental shelf

Aphotic Zone: area of water that lacks light

Photic Zone: uppermost layer of body of water that receives sunlight for photosynthesis

Zonation in Lakes

Littoral Zone: shallow waters along shores, where flowering plants are rooted

Limnetic Zone: offshore and comprises water that receives enough light to support photosynthesis

Aquatic Biomes: Lakes and Ponds

• found at high latitudes, formed by glaciers

• water movement and seasonal turnover driven by wind and changes in temp (top goes to bottom, and vice versa)

• organisms adapt based on depth and sunlight availability

Aquatic Biomes: Freshwater Wetlands

• shallow-water habitats where soil is saturated in water for parts of year

• Wetlands distinct from lakes and ponds due to:

• only having shallow water

• has emergent plants that grow above surface of water

Aquatic Biomes: Streams

• streams and rivers move constantly in one direction

• streams are shallow enough to allow sunlight to reach bottom

• Structure of stream varies along length:

• where it originates it is cold, narrow, and fast

• at end, it is warmer, wider, and slower

Aquatic Biomes: Estuaries

• an estuary forms when a river meets the ocean and freshwater mixes with saltwater

• includes saline wetlands and nearby open, brackish (slightly salty) waters

• most productive environment on Earth; serve as fish nurseries, has abundant vegetation, invertebrates, and plankton

Aquatic Biomes: Oceans

• form a continuous body of salt water

• water movement is dominated by different processes at different depths:

• the intertidal and neritic zone are most productive (rich in sunlight and nutrients, supports algae)

• in neritic zone, upwelling current are most important (brings cold, nutrient-rich water from sea floor to surface)

Imagine you are doing a survey of some land and you find permanent, standing water. It has some surface plants, but the depth is 10-15ft deep in the middle and supports aquatic life below the ice in the winter. This would be a…

Lake/pond

Two big patterns in Biodiversity related to Biomes:

1) Latitudinal Gradient in Biodiversity

2) Species-Area or Biodiversity-Area Curve

Latitudinal Gradient in Biodiversity

species diversity (richness) often peaks at equator and declines towards poles

Ex 1. higher species of butterflies at equator (79-81) than at poles (3, 9, 13)

Potential Explanation for Latitudinal Gradient

(the Mid-Domain Effect)

• latitudinal gradient is a statistical artifact; poles place a bound on species ranges making it more likely to get more species near equator by CHANCE alone

Climate Hypothesis for Latitudinal Gradient in Biodiversity

more productivity causes more species

1) Warmer, wetter climates promote higher NPP

2) Higher NPP supports more individuals

3) More individuals beget more species by evolution

• tropics have more species, because they have higher NPP

• the poles have fewer species, because they have lower NPP

The Historical Hypothesis for Latitudinal Gradient in Biodiversity

tropics are older and thus have more species

• ancient world was warmer, and tropical habitats were global norm

• since tropics are older than poles, biodiversity had more time to accumulate species in tropics

Second Pattern: Species-Area Relationship

larger areas contain more species than smaller areas

What is the relationship between size of habitat and colonization or extinction of species in that area?

number of species on an island reflects equilibrium, where:

• immigration of new species (+ Biodiversity)

• extinction of resident species (- Biodiversity)

Extinction and Colonization Rates on Islands

• Extinction Rates are higher on Small Islands

• Colonization Rates are higher on Large Islands

Why are Larger Islands more important?

• larger ‘islands’ are needed to preserve species, more connectivity

Define Population Density. Example?

is the number of individuals of a species per unit area (abundance)

Ex.

• the number of oak trees per square kilometer in a forest

• the number of isopods per cubic meter in soil

• the number of Daphnia per liter in a pond

Distribution within a population may be:

• Clumped (underdispersed)- grouped in patches

(school of fish)

• Uniform (overdispersed)- individuals equally spaced in environ. (penguins)

• Random- individuals are spaced in an unpredictable way

(flowers)

Calculating Population Size for Sedentary Species

counted via:

• lines of known length called transects

• plots of known size called quadrats

• counts used to estimate population size and document trends over time

Calculating Population Size for Mobile Species:

• harder to count as numbers along transect can change as individuals move

• if individuals can be captured and tagged, size of population can be estimated using mark-recapture method

Mark-Recapture Method Example

• Mark 100 Individuals

• Randomly capture 30 individuals (15 marked)

• Population size is 200

N= # of marked in first catch * total number of second catch/Number of marked in second catch

Demography

study of birth rates, death rates, age distributions, and size of popul.

• Number of individuals present in popul. depends on:

• Birth

• Death

• Immigration (In)

• Emigration (Out)

How does a population fluctuate considering the four processes?

(Birth, Death, Immigration, Emigration)

• Population Growth (increases) with Birth or Immigration

• Population Declines (decreases) with Death and Emigration

What are the Two Major Factors in Demography?

• Age-specific survivorship (l_x)

• Age-specific fecundity (m_x)

Define Survivorship

the proportion of offspring produced that survive, on average, to a particular age

• plots logarithm of # of survivors vs age

Types of Survivorship Curves and Examples

Type I curve: high survivorship throughout, most individuals approach maximum life span

(Ex. orangs, elephants, whales, wolves, chimpanzees)

Type II curve: constant rate of survivorship over time (turtles)

Type III curve: high death rates early in life but high survivorship after maturity (fish and rats)

not all individuals of a species follow the same survivorship curve; females also tend to have higher survivorship than males

Fecundity and Age-Specific Fecundity

• Fecundity is the number of female offspring produced by each female in the population

• Age-specific fecundity: average number of female offspring produced by females in each age class

• uses survivorship curves and has variation

Life Tables

summarize probability that an individual will survive and reproduce at any interval over its lifetime

• uses age-specific values for fecundity (m_x) and cumulative values for survivorship (l_x)

What does ‘l_xm_x’ represent on a Life Table? R?

• l_xm_x represents the offspring produced at each age per female

• R is the total number of offspring produced per individual

What is the Reproductive Rate Equation?

N_t+1=N_tR

• N_t+1= population size at next gen

• N_t= population now

• R= Net Reproductive Rate (indicates whether population is increasing or decreasing)

Life history

the pattern of survival and reproduction events during the life of an organism

• studied to observe how life tables vary among populations with different abiotic and biotic components

• Ex. The study on beavers identified that there is a high mortality when juvenile beavers first start leaving the den

What are Fitness Trade-Offs?

Fitness Trade-offs occur because every individual has a restricted amount of time and energy at its disposal (has limited resources)

• Ex. if a female devotes a lot of energy to producing many offspring, she cannot devote same energy to growth

• Female maximizes fecundity, maximize survival/growth, or find a balance between the two

What does an organism’s life history describe?

• how an individual allocates resources (includes survivorship, age-specific fecundity, age at first reproduction, growth rate)

• life history is shaped to maximize individual’s fitness in its environment

Explain the Life-History Patterns (Survivorship and Fecundity)

High Fecundity and Low Survivorship:

• many, small offspring

• early maturity

• small body

• low disease and predator resistance

• short life

Low Fecundity and High Survivorship:

• few, large offspring

• late maturity

• large body

• high disease and predator resistance

• long life

Sequence of Counts in Population

N₀, N₁, N₂, N_3, N₄, N_5…

• N_t= Population Size at Time/Generation t

For Example:

N₀=8, N₁=191, N₂=201, N₃=161, N₄=156, N₅=137

How many fish will there be after 10 generations?

How many total fish will have died after 10 generations?

• Sequence of counts= N_t=N₁₀

• N_t=b^tN₀ where b is the birth rate of daughters

Answer:

• t=10

• b=2

• N₀=1

• N₁₀= (2¹⁰)(1)= 1,024 alive

• N₁₀ (dead)=(N_t-1)—>1,0124-1=1,023 dead

Model of Population Growth Equation

N_t=b^tN₀

• t= number of generations

• b= birth rate

• N₀= initial population size at generation 0

Model of Population Growth with a Death Rate, d

N_t=(1+b-d)^t N₀

• t= generations

• b= birth rate

• d= death rate

• N₀= initial population size at generation 0

Population’s Overall Growth Rate (change in population size per unit in time)

ΔN/Δt= Births - Deaths + Immigrants - Emigrants

What is the Population Growth Equation when no immigration or emigration is occurring?

ΔN/Δt= B - D

Ex. A population of 1,000 rabbits

• over 1 year, there was 100 births and 50 deaths

• =50 rabbits a year

Population Growth Equation expressed per individual in population in reference to

(ΔN/Δt= B - D)

ΔN/Δt= bN-dN

• Per capita birth rate (b)= 100/1,000=0.10

• Per capita death rate (d)= 50/1000=0.05

• ΔNΔt= (0.10×1000) - (0.05×1000)

Exponential Growth Equation

• used to calculate per capita growth rate at a given moment in time (present, instantaneous)

• dN/dt=rN

• where r simplifies b and d

• r>0, growing

• r<0, declining

• r=0, stays the same (at equilibrium)

R=rN=(ΔN/Δt) = Population Growth Rate

• r= per capita growth rate, when is r is known, ask: how many individuals, N, are in popul.? (N needed for rN= Population Growth Rate

• R= population growth rate (if you know R, you know Population Growth Rate

Exponential Population Growth Model

when growth with r>0 is plotted graphically, a J-shaped curve is shown (as the r becomes larger, the slope of the curve becomes steeper, r is also constant)

• Equation: dN/dt = rN

When does Exponential Growth occur?

occurs when resources are not limiting

• does not depend on density (density-independent)

Basic Equation for Exponential Growth

R=rN=ΔN/Δt

• what one individual adds = per capita population increase = r

• what all N individuals add = total population growth = R

Ex: Per capita birth rate (b) = 100/1,000 = 0.10

Per capita death rate (d) = 50/1,000 = 0.05

• where r simplifies b and d

ΔN/Δt = (0.10 x 1000) – (0.05 x 1,000)

= (0.10 – 0.05)1,000 = 50 per year

Per Capita Growth Rate Equation

Divide R (Population Growth Rate) by N to get r, the “per capita” Growth Rate

r= ΔN/Δt=R/N= Per Capita Growth Rate 

(1/N means “per capita” or “per individual”)

1st way of Graphing Exponential Growth

Plot population size, N, against t, time

• Population Size increases with time and makes a J-shaped Curve of exponential growth

2nd way of Graphing Exponential Growth

Plot R= ΔN against N_t

• Population Growth Rate, R, is proportional to Population size or Density

(more individual = more growth)

Example from rabbits:

0.05 x 1000 = 50 per year

0.05 x 2000 = 100 per year

0.05 x 3000 = 150 per year

0.05 x 4000 = 200 per year

3rd way of Graphing Exponential Growth

Plot R/N_t or ‘r’ against N_t

• Population Growth Rate per capita, R/N, is constant as population size or density changes. Density, N, does not affect the birth or death rate.

Assumptions of the Exponential Growth Model

• Per capita rate of increase, r, is constant

(birth and death rates are constant)

• No emigration or immigration

• Either no age structure, or a stable age structure

• No genetic variation in growth rate

• shows J-shaped curve of Population (N) over time