Chapter 8: Ecology Study Guide

Ecology

the scientific study of how organisms interact with their environment and other organisms

Organismal ecology

• focuses on how an organism's structure, physiology, and behavior reacts to challenges in its environment

  • Organism: single living thing 

Population ecology

• Population ecology analyzes factors that affect population size and its changes over time

  • Population: a group of individuals of the same species living in an area,

Community Ecology

• Community ecology is the study of interactions between species and how they affect community structure and organization

  • Community: populations of different species living in a specific area, close enough to potentially interact with one another 

Ecosystem Ecology

• focuses on energy flow and chemical cycling between organisms and their environment (abiotic and biotic factors) 

  • Ecosystem: a community of organisms in an area and the physical factors that they interact with

Landscape (seascape) Ecology

• examines factors controlling energy, material, and organism exchanges across ecosystems 

  • Landscape: a variety of connected ecosystems

Global ecology

• studies the regional exchange of energy and materials and how it affects the functioning and distribution of organisms across the biosphere

  • Biosphere: global ecosystem, all the plant ecosystems and landscapes

Biotic factors

• Biotic factors: Other living species in an ecosystem

  • Examples of interactions between biotic factors: predation, pollinators, parasites

  • Examples of biotic factors: trees, fungi, etc

Abiotic factors

• Abiotic factors: the physical conditions of an area

  • Ex: temperature, amount of water and oxygen present, salinity, sunlight present, etc -- anything that makes up and affects the composition of an area.  

Population density

• Population density: individuals per unit area or volume 

  • Changes, not a static number

  • Density is calculated by finding the average density of plots and using the average to estimate for a whole population. 

Factors that affect population density

• BIDE Model

  • Increase through birth and immigration

  • Decreases through emigration and death

• Formula: Total population = birth + immigration - death - emigration

Per capita growth rate

• Per capita growth rate: the rate at which the population changes (grows or declines) per individual.

  • Birth rate - death rates 

• Per capita growth rate is utilized to calculate the population growth at each moment in time, rather than a specific time interval, such as one year

• R-max: intrinsic rate of increase - maximum rate of population growth without exceeding carrying capacity 

Exponential Growth

• Exponential growth: population growth model under ideal conditions - members have access to abundant food, and are free to reproduce at their capacity 

  • Increases at a consistent rate, creating a J-shaped growth pattern 

  • It can occur in newly introduced populations or those that have suffered a catastrophic event 

Logistical Growth

• Logistical growth: population growth that levels off and stabilizes once the carrying capacity is reached 

  • Usually, a delay occurs before the negative effects of the population are shown 

    • Therefore, they may overshoot capacity temporarily

Carrying Capacity

• Carrying capacity: the maximum population size that a particular environment can sustain 

  • Varies over time, as realistically, resources are not infinite

  • Limits exponential growth, shifting it into logistical growth 

Three patterns of dispersion

• Dispersion: pattern of spacing among individuals within the boundaries of the population, affected by environmental and social factors 

  • Clumped: Individuals aggregated in patches where factors are favorable 

    • It can be associated with food location, mating behaviors, and can affect predation or defense of the species

  • Uniform: evenly spaced pattern 

    • Results from interactions - territoriality to defend their area from other individuals who compete for the same resources

  • Random: unpredictable spacing, individuals are independent of each other

    • Occurs in the absence of attraction between other individuals 

Density Dependent Factors

• Density Dependent Factors: When birth/death rates are controlled by the density of the population

  • Ex: How much food is available (more of a species means less food for each individual)

  • Limits how large a population can get

Density Independent factors

• Density Independent Factor: When birth/death rates are not controlled by the density of the population

  • Ex: A natural disaster (can affect the size of the population, but is not caused by the population density)

Life Tables

• Life table: summarizes the demography, or survival and reproduction rates of individuals in specific age groups within a population

  • Constructed through research where scientists followed a cohort from birth to death

    • Typically, focus on the females for reproduction 

Cohort

a group of individuals of the same age

Survivorship curve

• Survivorship curve: the graphic representation of the survival rate in a life table

  • Plot of the proportion in a cohort alive at each age

  • Type 1: Large mammals (elephants) and humans

    • Flat during early and middle age, then declines among older ages

    • Produce a few offspring, but provide them with good care

  • Type 3: plants, fish, etc

    • drops sharply, dying young, then flattens out as those that survive the early die-off period develop 

    • Organisms with large offspring production provide little care 

  • Type 2: rodents, annual plants, lizards

    • Intermediate, constant death rate over the organism's life span

K-selection

• K-selection: selection of traits that are advantageous in high-density environments (near resource limit, where competition is stronger)

  • Organisms have fewer offspring, but they are more likely to survive to a reproductive age, as a large amount of care is put into them 

  • Maximizes K, the carrying capacity

    • Some traits: few offspring, long life span, slow development, high parental care 

R-selection

• R-selection: Selection for traits that maximize reproductive success in low-density environments (with low competition)

  • Organisms have more offspring, but they are less likely to survive to a reproductive age

  • Maximizes r, the intrinsic rate of increase/per capita growth rate 

    • Some traits: high reproductive rates, small bodies, short lifespans, early maturity

R and density

• R and density can be related through the k vs r selection

  • R selection occurs in areas of low density, and r is maximized 

    • As r increases, density increases 

  • K selection occurs in areas of low density, focusing on traits near the carrying capacity

Ecological Niche

refers to the biotic and abiotic factors used by organisms in an environment

Interspecific competition

Where individuals of different species compete for the same necessary resources that impact both species' fitness. 

Intraspecific competition

occurs when members of the same species compete for the same resources 

Resource partitioning

• Resource partitioning: Differentiation of ecological niches that enables species to coexist in a community

  • If they have one or more large differences in their niches, done through evolution by natural selection, species can coexist

Competitive exclusion

• Two species whose members compete for the same resources cannot coexist permanently

  • Conclusions from Russian ecologist G. F. Gause

  • Members of two species that compete for the same limiting resources can not co-exist in the same area forever

  • Without any changes in the environment, one species will have an advantage and will eliminate the inferior competitor 

Exploitation

any +/- interaction where individuals of one species benefits by feeding on (harming) individuals of another species 

Character Displacement

• Character displacement: the tendency for characteristics to diverge more in sympatric than allopatric populations of species

  • Allopatric: closely related species whose populations are geographically separate

    • Species have similar structures and use similar resources

  • Sympatric: closely related species whose populations are geographically overlapping

    • Show differences in form and resources used 

Predation

• Predation (+/-): A type of exploitation where an individual of a species, the predator, kills and consumes another individual of a species, the prey.

  • Predators have sharp senses, claws, or other adaptations such as agility that allow them to catch their prey. 

  • Prey have behavioral defenses, such as instincts to hide, flee, and, less commonly, self-defend

  • Also, they have physical adaptations, such as their coloring (camouflage), chemical defenses like toxins, or physical defenses, like spikes, to make it harder for predators. 

  • Both predators and prey can mimic other species    

    • Ex: Cheetahs and impalas (antelopes), where the cheetahs' speed fights against the agility of the impalas. 

Mutualism

• Mutualism (+/+): Interactions that benefit both organisms, but also cost each organism something  

  • Ex: Coral and algae: Coral provides nutrients and shelter for the algae, and in return, the algae produce synthesized sugars that the coral can feed on 

Commensalism

• Commensalism (+/0): Where one individual of a species benefits, while the other experiences no changes

  • Many interactions have the potential to change, and commonly, those that are commensalism can change to become mutualism. 

  • Ex: barnacles and whales, where the barnacles attach to the whale's skin and achieve a wider range of food through the whale's movement. 

Herbivory

• Herbivory (+/-): an exploitative interaction where a herbivore eats plants or algae, harming them while not killing them. 

  • Insects that are herbivores have chemical sensors that help them determine the plant. Other species have a keen sense of smell, or special teeth or digestive systems to help process plants. 

  • Plants' defense can include self-produced toxins or physical structures, such as spikes, to harm the herbivore. 

    • Ex: koalas and eucalyptus: koalas mainly eat the leaves of the eucalyptus tree

Parasitism

• Parasitism (+/-): Exploitation, where an organism (parasite) takes nutrients from another organism (host), harming the host's fitness levels and species density. 

  • An estimated ⅓ of Earth's species population is parasites

  • Parasites within an organism are called endoparasites, while those that feed off the external body are called ectoparasites. Another kind is a parasitoid, which is an insect that lays eggs on the host.

  • Many parasites use multiple hosts or change the host's behavior to obtain their next host

    • Tapeworms attach themselves to the inside of the host's intestines, such as a human or cow, and receive food by consuming the host's half-digested food. This causes the host to lose its nutrients.

Biomass

• Biomass: the total mass (energy, nutrients, etc) of all organisms in a given area

  • It is stored as chemical energy by primary producers through photosynthesis → which is then consumed by herbivores, moving up the trophic levels (trophic efficiency) 

  • Generally referred to as the total biomass production at each trophic level

Trophic levels

Trophic levels: an organisms position in the food chain

• Primary producers (autotrophs), most of which are photosynthetic, convert light energy into biomass 

  • Includes plants, algae, and some photosynthetic prokaryotes

• Primary consumers: heterotrophs, more specifically herbivores that eat the producers

  • Also includes decomposers or detritivores

• Secondary consumers: carnivores, who eat the herbivores

• Tertiary consumers: The carnivores that eat other carnivores 

Decomposers or detritivores

• A type of heterotroph that gains energy through detritus, or dead organic material

• Have enzymes to digest material and absorb broken-down products

• Recycle organic matter from all trophic levels into usable inorganic compounds by primary producers

  • When they die, the compounds return to the soil, to be reused

• The secondary consumers also eat decomposers, passing chemicals from primary producers through the trophic levels.

Food chains

• Food chains: determine the transfer of energy from one trophic level to the next

  • starting with the energy in autotrophs, the primary producers, and moving to herbivores, primary consumers, carnivores, and finally decomposers. 

Food web

• Food web: network of food chains in an ecosystem, demonstrating how they are linked together

Introduced and Invasive Species

• Introduced species: non-native or exotic species are organisms that humans have moved to regions outside of their native locations

  • Can be intentionally to try and control various environmental issues or accidentally, harming the ecosystem 

  • Invasive species: an introduced species that spreads rapidly and causes harm to their environment 

    • They outcompete native species (leading to extinction) and disrupt the ecosystem

Species Richness and Relative Abundance

• Species richness: number of different organisms that make up a community 

• Relative abundance: the proportional abundance of the different species in a community 

  • More diverse communities (those with more species richness and abundance) are more stable, as they can better respond to environmental stress

Foundation Species

species that have large effects on their communities (other organisms) due to their large size or prevalence 

Keystone Species

• Keystone species: species that are not as abundant but have a large control over other trophic levels in their ecosystem due to their ecological niche or role in the community 

  • Bottom up: availability of food at lower trophic levels limits the abundance of organisms at higher trophic levels

    • Ex: if there are fewer nutrients for plants, herbivore numbers are lower, and therefore predator numbers are controlled as well

  • top down: abundance of organisms at higher trophic levels controls the abundance of organisms at lower trophic levels 

    • Ex: if whales (tertiary consumers) were removed, it would increase the abundance of otters (secondary consumers). 

Ecosystem Engineers

• Ecosystem engineers: species that create or drastically alter their physical environment

  • Some foundation species can also be ecosystem engineers 

Ecological Sucession

the process by which disturbed areas are colonized by a variety of species and then are replaced by other species over time

Primary and Secondary sucession

• Primary succession: when ecological succession begins in a lifeless area 

  • First, prokaryotes and protists are the only initial life forms. Soil and other mosses develop, and then plants colonize an area. This production may take hundreds, if not thousands, of years

  • ex: in an area of rubble left by a retreated glacier. 

• Secondary succession: The recolonization of an area after disturbance has removed organisms 

  • ex: Yellowstone after the fires in 1988, where many organisms were removed from the area. 

Primary and Secondary Production

• Primary production: the amount of light energy converted to chemical energy by autotrophs during a time period

• Secondary production: the amount of biomass that heterotrophs convert into their own biomass during a given time period

GPP

Gross primary production: total primary production and amount of energy from light converted to chemical energy in an ecosystem per unit time

NPP

• Net Primary Production: The amount of chemical energy that remains after the autotroph’s respiration and is available for consumers

  • GPP minus energy used by the primary producers in cellular respiration 

  • About half of GPP

• NPP can also be expressed as the new biomass added in a given unit of time. 

  • This provides insight into the productivity of different ecosystems

Autotrophs vs Heterotrophs

• Autotrophs: organisms that use light energy to synthesize food which is used for growth and energy 

  • Typically plants and other photosynthetic organisms

• Heterotrophs: depend directly or indirectly on autotrophs for energy and food → cannot create food on their own

Energy Flow in an ecosystem

• Energy flow: begins when sunlight enters and is converted into chemical energy by autotrophs 

  • It is then passed to the heterotrophs as they consume other organisms who take it in as the organic compounds

  • Passed along the trophic levels from primary consumers to tertiary consumers 

  • As energy moves, it is gradually lost as heat and is dissipated as heat

    • Only moves in one direction, and cannot be recycled 

Trophic efficiency

• Trophic efficiency: the percentage of production transferred from one level to the next

  • On average, it is about 10% - 90% of the energy available at one level that is not transferred to the next level

    • Rest is lost 

  • As you go up in topic levels, biomass goes down

Biogeochemical cycles

• Chemical elements are only available in limited amounts → life depends on the recycling of chemical elements

• Biogeochemical cycles: the movement of chemical elements between the abiotic and biotic components of the biosphere

  • Two categories: global and local

• Humans have a large effect on the global carbon and nitrogen cycles 

Water Cycle

• Water cycle: water is essential for all organisms → if it is not available, it affects rates of ecosystem functioning

  • All organisms can exchange water with the environment directly 

  • Liquid is its primary phase

    • Some organisms can harvest water vapor

    • Frozen soil water can limit terrestrial plants

  • The ocean has 97% of water - the rest comes from glaciers, lakes/and rivers

  • The main process 

    • The evaporation of water by solar energy, 

      • Transpiration by terrestrial plants moves water through their stoma into the atmosphere 

    • Condensation of water vapor into clouds, 

    • Precipitation: rain 

    • Percolation: movement of water through soil or other porous materials

    • Surface and groundwater flow is returned to the oceans

Phosphorus cycle

• Phosphorus cycle: organisms use phosphorus to compose nucleic acids, phospholipids, ATP and more

  • The most important inorganic form is phosphate, which plants absorb and use to synthesize organic compounds

  • The largest reservoir is sedimentary rocks of marine origin as well as soil 

    • Soil particles bind to phosphate; therefore, most of the phosphorus recycling is localized in ecosystems 

  • Processes: 

    • weathering rocks adds phosphate to the soil, moving into water that eventually reaches the sea

    • Phosphate is taken up by producers and added to biological molecules eaten by consumers 

    • Phosphate is returned to the soil through the decomposition of biomass or excretion 

    • No significant phosphorus-containing gases → small amounts move towards the atmosphere in the forms of dust or sea spray

Nitrogen Cycle

• Nitrogen cycle: Nitrogen is part of amino acids, nucleic acids, and proteins, a limiting plant nutrient 

  • Plants use two inorganic forms of nitrogen: ammonium and nitrate

    • Also, use organic forms like amino acids 

  • Animals can only use organic forms, and bacteria can use all and nitrite 

  • The main source of nitrogen is in the atmosphere 

    • Other places include soils, sediments in bodies of water, and biomass

  • Processes

    • Nitrogen enters an ecosystem from the atmosphere through nitrogen fixation or natural fixation 

      • Lightning and volcanic activity fix nitrogen naturally (turning N2 into NO3 - nitrate)

    • Nitrogen fixation: the conversion of nitrogen gas (N2) to form that are usable (NH3-, ammonium)

      • Humans input more nitrogen than natural inputs

    • Nitrification: Ammonium is converted into nitrite (NO2) and then nitrate (NO3) by nitrifying bacteria

    • Assimilation: plants use ammonium and nitrate from the soil and add rhythm to organic compounds → animals obtain nitrogen by eating them

    • Ammonification: decomposers convert nitrate from detritus (dead animals) and waste into ammonium → ammonium then goes to nitrification to be converted into nitrate again

    • Denitrification: Denitrifying bacteria converts nitrate in the soil into nitrogen gas (N2), releasing it into the atmosphere - completing the cycle

      • Excretion (pee) also releases nitrogen back into the atmosphere

Carbon Cycle

• Carbon cycle: Carbon contributes to many of the essential organic molecules for organisms 

  • Photosynthetic organisms use CO2 in photosynthesis → converting it to organic compounds that are usable by other organisms

  • Respiration allows all organisms to return carbon to the environment

  • Carbon comes from fossil fuels, soil, biomass, and the atmosphere; the largest source is limestone

  • Process: 

    • Photosynthesis by plants and phytoplankton removes CO2 each year

    • The same amount is added to the atmosphere through CR by producers and consumers 

      • Burning of fossil fuels + wood also adds more 

      • decomposition: decomposers break down organic matter, which also releases CO2

Bioremediation

• Bioremediation: ecologists add organisms, typically prokaryotes, to detoxify polluted ecosystems 

  • Ex: a lichen species that concentrates uranium, making it easier to observe and collect

Biological Augmentation

• Biological Augmentation: ecologists add organisms to add essential materials to a degraded ecosystem  

  • Lupines, which are nitrogen-fixing plants, are often added to alpines to add more nitrogen to the soil → benefiting other native plants so they can obtain enough through the soil 

First law of thermodynamics

• First law of thermodynamics: energy cannot be created or destroyed but only coverted from one form to another

  • Photosynthetic organisms convert solar energy into chemical energy, but the amount doesn't change 

Second law of thermodynamics

• Second law of thermodynamics: Every exchange of energy increases the entropy of the universe 

  • Energy conversions are inefficient, and some is always lost as heat 

  • Energy does not stay for long periods of time; as it flows, it is lost as heat 

    • turns into an unusable form

  • Heavily reliant on the sun's constant supply of energy

Law of conservation of mass

• The law of conservation of mass: Matter cannot be created nor destroyed 

  • allows the determination of how much chemical elements cycle within an ecosystem 

  • Chemical elements are recycled, unlike energy, which can not be reused    

  • Can be gained or lost 

Ecological changes linked to climate change

• Species relocation: species have shifted their geographic locations as the climate has changed

  • Ex: some butterfly species in Europe have shifted farther north as the climate has warmed

• Ocean acidification: increased CO2 levels in the ocean, and they have also started releasing more than they absorb 

• Forrest fires: more droughts and higher temperatures have increased the risk of fires

• Habitat loss: Due to the ice caps melting, many arctic species have lost their habitats

Three levels of biodiversity

• Genetic diversity: Genetic diversity exists within a population and between populations

  • enables adaptation to environmental change 

• Species diversity: Within a species, genetic information is generally similar, but across different species, it differs slightly  

  • maintains communities and food webs 

  • Endangered species and population extinction can lead to a lack of species diversity

• Ecosystem diversity: different ecosystems require different traits and, therefore, different genes 

  • There is a variety of ecosystems, and due to different interactions between species, extinction can affect ecosystems

Endangered vs Threatened Species

• Endangered species: one that is in danger of extinction throughout all or most of its range

• Threatened species: one that is likely to become endangered in the future 

Biological Magnification

• Biological magnification: a process in which substances, for example, toxins, become more prevalent as they move up the trophic levels

  • The amount of toxins (accumulated in the fat of organisms) is magnified

    • A shark will eat many fish that each have toxins, therefore accumulating toxins up the trophic levels

Critical Load

• Critical load is the amount of added nutrients that can be absorbed by plants without harming an ecosystem's integrity  

  • Problems arise when the critical load is exceeded

Climate Change

a directional change to the global climate that lasts for 30+ years due to excess carbon in the atmosphere  

The greenhouse effect

• The greenhouse effect: the warming of the earth due to the accumulation of CO2, methane, and other gases in the atmosphere, which absorb infrared radiation the earth emits, radiating it back to the earth

  • This process retains solar heat, causing a rise in temperature

Global Footprint

• The carrying capacity of the Earth for humans is uncertain; however, we are using many resources in an unsustainable way 

• The sustainable global footprint for each person is 1.7 gha, while globally the average footprint is 2.7 gha

Additional Information

• Production efficiency: percentage of assimilated energy that organisms convert into biomass

  • Ectotherms: dont generate internal heat so greater percentage of assimilated energy goes into making biomass

  • Endotherms: uses more energy to maintain body heat so need more energy to make biomass