Chapter 36. Ecology
Recommended Articles : 【Biology】 Biology Table of Contents
1. Population
2. Community
3. Ecosystem
1. Organism → Population → Community **→** Ecosystem
⑴ Population : All individuals of a species living in a particular area.
⑵ Density fluctuations in populations
① Factors of increase : High birth rate, immigration
② Factors of decrease : High death rate, emigration
⑶ Survival of populations
① Type I survivorship curve : High death rate in old age
② Type II survivorship curve
③ Type III survivorship curve : High death rate in youth
⑷ Population structure
① Population structure : Characteristics of density and spatial distribution
② Measurement of population size : Census, mark-recapture method, quadrant method, transect method, sample plots, etc.
○ Quadrant method : Placing a quadrant frame in the survey area to count individuals
Figure. 1. Quadrant method
○ Density = Number of individuals ÷ Total area : A is 10/25, B is 4/25, C is 6/25
○ Relative density = Number of individuals ÷ Total population size : A is 10/20, B is 4/20, C is 6/20
○ Frequency = Number of times the species appeared in the sample ÷ Total number of samples : A is 6/25, B is 4/25, C is 6/25
○ Cover = Area occupied by a species ÷ Total area
○ Importance : Sum of relative density, relative frequency, and relative cover
○ Species richness
○ Species diversity
○ Dominant species : The most abundant species that has the greatest impact. These species have high biomass or numerous individuals and exert significant effects on the community.
○ Keystone species : Species that have a disproportionately large effect on their environment despite their low abundance. They play a crucial role in maintaining ecosystem structure and function.
○ Indicator species : Species that are indicative of a specific community or habitat condition.
○ Rare species : Species with low abundance within a community.
○ Foundation species : Species whose presence influences the presence of other species. Their removal can lead to the extinction of other species.
○ Pioneer species : Species that create a new habitat environment (e.g., beavers)
③ Spatial distribution of populations
○ Clumped distribution : High density where resources are abundant
○ Uniform distribution : Species that establish territories
○ Random distribution : Species with wide environmental tolerances, no specific factors for distribution
④ Limitation 1. Excessive population growth leads to high mortality rates: High risk of extinction
○ Density-dependent factors : Resource scarcity, increased disease, pollution
○ Density-independent factors : Droughts, extreme temperatures, natural disasters, etc.
⑤ Limitation 2. Time lag between birth and reproduction of individuals → Immediate environmental impacts not evident
○ Demographic lag : Time interval between the decrease in birth rate and the decrease in population growth rate
⑵ Logistic population growth model : Complements Limitation 1.
① The growth rate of the population per unit time depends on the population size and environmental resistance
○ Carrying capacity (K) : Maximum population that an environment can sustain
○ Environmental resistance : Corresponds to 1 - K/N for population size N
○ ∴ dN/dt = rN(1 - N/K)
② r-selection: High population growth rate, small body size, large number of offspring, short generation time
○ Environmental resistance approaches 0, follows a J-shaped exponential growth model to some extent : Density-dependent growth
○ Characteristics of J-shaped curve. Emphasis on reproduction. Short lifespan, small body size
③ K-selection: Low population growth rate, large body size, fewer high-quality offspring
○ Population growth rate nears 0 as the population approaches the carrying capacity (K)
○ Long lifespan, large body size, iteroparity, extended development time, intense competition between individuals
○ Organisms under K-selection tend to reproduce at a later age. Fewer offspring and smaller population size
Figure. 2. Population growth models
(A) represents the exponential growth model, (B) represents the logistic population growth model
⑷ Demographic transition : Growth rate increases due to a decrease in death rate despite no change in birth rate
① Pre-industrial revolution: Both birth and death rates were high in most countries
② Post-industrial revolution: Improved hygiene and medical advances led to a decrease in death rate
③ The time delay between death and birth rates significantly affects population size
④ Many developing countries are in the demographic transition phase → Pursuit of population control policies
⑤ Developed countries have transitioned, resulting in low population growth rates → Focus on childcare, education, welfare, and immigration policies
Figure. 3. Demographic transition
2. Organism → Population → Community **→** Ecosystem
⑴ Community : An assemblage of all populations of organisms living close enough together for potential interaction.
⑵ Food web : Interactions involving eating and being eaten
① Ecological niche : The role a species plays in an ecosystem, which encompasses the biological and physical resources it uses
○ Influenced by habitat and food type
○ Fundamental and realized niches may differ based on environmental conditions
② Species within a community occupy unique ecological niches and interact
○ Ecotypes : Differentiated by adaptation to different environments within the same species
③ Interactions within communities
○ Interaction 1. Mutualism (+/+) : Both species benefit from the interaction
○ Examples: Bees and flowering plants, large fish and cleaning fish, ants and acacia trees
○ Example: Legumes and root-nodule bacteria
○ Example: Fungi and plant root interactions in mycorrhizae
○ Interaction 2. Commensalism (+/0) : One species benefits while the other is neither helped nor harmed
○ Interaction 3. Predation (+/-) : Process of one species capturing and eating another
○ Example: Plant → Insect → Bird
○ Lotka-Volterra model : Describes predator-prey interactions resulting in oscillations in population sizes
Figure. 4. Lotka-Volterra model
○ Formulation : For the ith species with population ni, weight ri, and interaction coefficient Ai←j for the jth species affecting the ith species,
○ Interaction 4. Parasitism (+/-) : Parasites gain nutrients from their host
○ Endoparasites : Internal parasites, such as ticks and malaria
○ Ectoparasites : External parasites, such as ticks
○ Interaction 5. Amensalism (0/-) : One species is harmed while the other is unaffected
○ Interaction 6. Competition (-/-) : Competition for the same resources
○ Examples: Mosquitoes, snails, tadpoles competing for resources in a pond
○ Supplementary 1. Competitive exclusion principle
○ Competition between two populations for limited resources, leading to competitive exclusion if severe
○ Competitive exclusion : One species prevents another from occupying a particular ecological niche through competition for resources and space
○ Example: Preventing the settlement of Salmonella enteritidis in a chick’s gut
○ Newly hatched chicks lack bacteria in their intestines
○ Untreated : Chick intestines have very few bacteria, leading to active S. enteritidis infection
○ Beneficial bacteria intake : Beneficial bacteria form a colony on the internal surface of the intestines
○ Exposure to Salmonella enteritidis
○ Untreated : Active S. enteritidis infection occurs
○ Beneficial bacteria intake: Salmonella enteritidis is expelled without finding a suitable colony site on the intestines
○ Supplementary 2. Mimicry
○ Batesian mimicry : Edible and non-poisonous species mimic the model that is unpalatable and poisonous
○ Müllerian mimicry : Several non-edible species evolve to resemble one another, reinforcing avoidance by predators
○ Supplementary 3. Hamilton’s rule
○ B : Benefit gained by the recipient, i.e., the expected number of offspring that survive
○ C : Cost paid by the altruist, i.e., the decrease in the number of offspring due to death
○ r : Coefficient of relatedness between the interacting individuals, i.e., the probability of sharing a particular allele
○ When B × r > C, altruistic behavior is favored.
○ Supplement 4: Edge Effect
○ The edge of the available boundary area shows different habitat characteristics from the interior area.
○ Characteristic 1: Competition frequency with other habitats is higher at the edge.
○ Characteristic 2: If the habitat was a forest, increased wind influence, temperature increase, humidity decrease, and light intensity increase.
○ As a result, edge species originating from adjacent areas have an advantage in inhabiting the edge rather than internal species.
○ Supplement 5: Habitat Fragmentation
○ Definition : Gradual destruction of habitats due to human activities, resulting in smaller and isolated habitats.
○ Outcome 1: Only populations of organisms that can survive in small habitats can persist.
○ Outcome 2: Increased edge effect.
④ Roles within a Cluster: Producers, Consumers (Predators), Decomposers
○ Producers : Increase energy levels within the cluster, green plants that synthesize organic matter from inorganic substances through photosynthesis.
○ Consumers : Decrease energy levels within the cluster, animals that consume organic matter for sustenance.
○ Decomposers : Decrease energy levels within the cluster, organisms that decompose animal and plant remains or waste, mainly microorganisms.
⑤ Keystone Species : Species that play a crucial role in determining the structure of an ecosystem
○ Example : Starfish feed on mussels, and if the keystone species starfish were absent, mussel populations would explode, leading to ecosystem destruction.
⑥ Ecological Energy Flow : Only a portion (~10%) of energy is converted to the next trophic level in a nutritional chain.
○ Solar energy availability and water usage are important factors in energy flow.
○ Diversity also influences energy flow.
○ Example : Prairies support a large biomass.
⑶ Nutrient Cycling : Recycling of inorganic nutrients through the food web
① Nutrient Efficiency : The ratio of energy transferred from one trophic level to the next, typically around 10%.
② Nitrogen Cycling
Figure 5. Nitrogen Cycling
○ Nitrogen Fixation and Others : Atmospheric nitrogen (N2) → Ammonia (NH3) → Ammonium (NH4+)
○ Case 1: High-energy fixation (lightning, meteor impact)
○ Case 2: Nitrogen fixation (anaerobic conditions): Soil bacteria, rhizobia, azotobacter, actinomycetes
○ Case 3: Nitrogen from corpses or waste products
○ Nitrification Process : Ammonium (NH4+) → Nitrite (NO2-) → Nitrate (NO3-)
○ Nitrosomonas : Ammonium (NH4+) → Nitrite (NO2-)
○ Nitrobacter : Nitrite (NO2-) → Nitrate (NO3-)
○ Chemical synthesis : Nitrosomonas and Nitrobacter synthesize sugar using energy released during oxidation of organic matter.
○ Denitrification Process : Nitrate (NO3-) → Nitrogen gas (N2)
○ Denitrifying bacteria : Nitrate (NO3-) → Nitrogen gas (N2). Anaerobic chemoautotrophs. Use nitrite and nitrate as final electron acceptors instead of oxygen in the respiratory electron transport chain.
○ Plants can use either Ammonium (NH4+) or Nitrate (NO3-).
③ (Note) Increased phytoplankton lead to higher oxygen consumption by decomposers when decomposing their bodies, leading to water quality deterioration.
⑷ Extinction
① Extinction : Complete disappearance of a species.
② Measurement of Extinction Rate
○ Extinction Rate : Percentage of species that go extinct each year from the total.
○ Background Extinction Rate : Rate at which species naturally go extinct due to evolutionary processes, 0.0001% per year.
○ Current Extinction Rate : 0.0037% per year, implying clear human involvement.
③ Cause 1: Habitat Destruction
○ Population growth increases pressure on natural areas.
○ Species-Area Curve : Number of species an area can support.
④ Cause 2: Habitat Fragmentation
○ 1st. Reduces the area for producer organisms.
○ 2nd. Higher-level consumers require more energy and larger habitats, leading to increased environmental pressure.
○ 3rd. Decrease in population of higher-level consumers.
○ 4th. Inbreeding of higher-level consumers promotes extinction.
⑤ Cause 3: Invasive Species
○ Invasive Species : Organisms newly introduced by human activity.
○ Lacks predators due to not co-evolving with local species, causing destruction.
○ Examples: Lionfish, cane toads, red-eared sliders.
⑥ Cause 4: Overexploitation : Using natural resources beyond their reproductive capacity.
⑦ Cause 5: Pollution
○ Herbicides threaten frogs and salamanders.
○ Agricultural fertilizer use → Eutrophication of water bodies leads to excessive algal growth → Massive fish die-offs due to oxygen depletion.
○ Carbon dioxide : Atmospheric pollutant associated with climate change.
⑧ Cause 6: Inbreeding : Example of the Irish Potato Famine 1847-1852
○ Cultivated the South American potato variant “lumper.”
○ Extinction Mechanism : Positive feedback loop
○ 1st. Small population → inbreeding, genetic instability
○ 2nd. Inbreeding, genetic instability → loss of genetic diversity
○ 3rd. Loss of genetic diversity → decreased adaptability and population fitness
○ 4th. Decreased adaptability and population fitness → high mortality, low reproduction
○ 5th. High mortality, low reproduction → smaller population
○ Potato famine mechanism
○ 1st. Potatoes reproduce asexually → genetic diversity = 0
○ 2nd. Potato blight fungus infects potatoes in the field
○ 3rd. Extinction of potatoes
○ 4th. Potato famine leads to 1.5 million deaths out of 9 million, with 1 million immigrating to North America.
3. Individual → Population → Community → Ecosystem (about biological kingdoms)
⑴ Ecosystem and Biome
① Ecosystem : Non-biological environmental factors (light, temperature, water, air, soil) + biological environmental factors
② Biome : Typical ecosystem spread over a wide geographical area
○ Biome : A large geographical area characterized by a dominant type of vegetation.
③ Energy in Ecosystems
○ Gross production : Total amount of organic matter produced by producers through photosynthesis, i.e., respiration + net production
○ Net production : Difference between gross production and respiration by photosynthetic organisms
○ Broken down into ingestion by consumers, egestion, defecation, growth, etc.
○ Consumption efficiency of primary consumers : Proportion of producer’s biomass consumed by primary consumers
○ Broken down into respiration, excretion, body remains, growth, etc.
○ Net community production : Difference between net production and respiration by heterotrophs
○ Production efficiency = Growth ÷ Ingestion
○ Homeotherms have low production efficiency due to energy spent maintaining temperature.
④ Pyramid of Numbers
○ Pyramid of individuals : Represents the number of individuals at each trophic level.
○ Pyramid of biomass : Diagram representing biomass (dry weight). Illustrates the food chain.
○ Pyramid of energy : Depicts energy flow, showing energy loss.
④ Ecological Succession (Plant Succession)
○ Stage 1: Succession : Gradual change of plant communities over time in the same location.
○ Stage 1-1: Primary Succession : Succession starting with no existing plant community.
○ Lichens become dominant species.
○ Stage 1-2: Secondary Succession : Succession starting with some existing plant community after disturbance like wildfire, with soil nutrients.
○ Grasses become dominant species.
○ Stage 2: Herb Stage → Shrub Stage → Climax Stage
○ Stage 3: Climax : Final stage of an ecosystem
○ Shade-intolerant species appear first, followed by shade-adapted species.
○ Biodiversity increases in the initial stages, then decreases.
⑵ Terrestrial Biomes : Determined by vegetation types - forests, grasslands, deserts, tundras
① Vegetation : Plant cover over the ground, “climate → vegetation” (∴ altitude, latitude dependent)
② Forests : Dominated by woody plants, cover about 1/3 of the Earth’s land surface and 70% of the Earth’s biomass.
②―① Tropical Rainforest : Strong sunlight, year-round 25-29°C, high rainfall (2500 + α mm), near or equatorial regions
○ High biodiversity, 750 species of woody plants per hectare → diverse habitats
○ Rapid decomposition of organic matter, plants rapidly reabsorb decomposed matter → organic material stored in soil decreases
○ Inorganic nutrients mostly fixed by plants, not suitable for agriculture without heavy fertilization
○ Lifespan of tropical forest farming is only 4-5 years, recovery takes decades
○ Tropical communities older than other communities → longer speciation periods → higher biodiversity↑
○ Generally, higher evaporation leads to greater biodiversity.
②-② Temperate Forest (Forest) : During the growing season, there is sufficient water (750 ~ 2500 mm) and light, but during winter ×, North-South 23° ~ 50°
○ Dominant Species : Deciduous Trees
○ General Succession : Weeds → Shrubs → Deciduous Trees → Deciduous Trees + Understory Plants
○ Region : Northern Hemisphere Mid-Latitudes, Australia
○ Deciduous : Evolution of leaf-shedding adaptation for moisture conservation, pigments that were previously hidden by sugars and chlorophyll are revealed during leaf decomposition
(Tannins, Anthocyanins, Carotenoids, etc.) lead to fall foliage
○ Understory plants grow rapidly and bloom while light is available
②-③ Coniferous Forest or Boreal Forest (Forest) : Winter -50 ℃, Summer 20 ℃, 300-700 mm, Exist near the poles (North America, Asia, Northern Europe)
○ Dominant Species : Conifers (e.g., Pine, Spruce)
**○ Largest group of organisms on Earth
○ Adaptation to long cold winters and humid summers
○ Evergreen Adaptation : Photosynthesis is limited in winter × → Chlorophyll is exposed when ice melts, enabling immediate photosynthesis
②-④ Mediterranean Shrubland (Forest) : Spring 10-12 ℃, Summer 30 ℃, Annual 300-500 mm (dry in summer), Mediterranean, Southern California, Southwestern Australia
○ Dominant Species : Evergreen Shrubs (e.g., Olive, Fig)
○ Adaptation to long dry summers and frequent fires → Fire adaptation (e.g., seeds germinate after exposure to high heat)
○ Example : Mediterranean regions experience hot and dry summers, and cool and wet winters
③ Grassland : Precipitation 250 ~ 500 mm, Dry months 8 ~ 9, Dominant in grasses
○ Example 1. Savannah : Tropical, Subtropical, Tropical Grasslands
○ Warm throughout the year
○ Example 2. Prairie : Temperate Grasslands (e.g., African Savanna, Hungarian Puszta, American Great Plains)
○ Winter averages below -10 ℃, Summer averages around 30 ℃
○ Dominant Species : Dominant growth from the base where herbivores nibble plants
○ During dry periods, periodic fires; during wet periods, restoration of grassland vegetation
④ Desert : Average 24 ~ 29 ℃, Precipitation less than 250 mm, Near latitudes 30° North/South
○ Significant temperature variations : -30 ~ 50 ℃
○ One-year life cycle : Adaptation to a complete life history in 2 ~ 3 weeks of rainy season
○ Plant Adaptations : Wax coatings, thorns, water storage in stem, adaptation to frequent fires
○ Desert Animal Adaptations : Kangaroo Rat, Nocturnal, Water loss prevention
○ Example : Kangaroo Rats are nocturnal, survive on metabolic water from breaking down fats in seeds
⑤ Tundra : Winter below -30 ℃, Short summer, below 10 ℃
○ Example : Northern Norway, Northern Canada
○ Plant growing season : About 2 months (50 ~ 60 days) in summer
○ Permafrost : Frozen ground, inhibits plant growth by preventing drainage
○ Plants grow low and flat due to strong winds and low temperatures
○ Effects of global warming : Some tundra areas are transitioning to coniferous forests
○ Tundra Animal Adaptations : Fat storage, fur, feather development, hibernation, migratory birds
Figure 6. Terrestrial Ecosystems
⑶ Aquatic Ecosystem
① Freshwater : Salinity below 0.1%
①-① Lakes and Ponds (Freshwater) : Bodies of water surrounded by land
○ May dry up seasonally, important habitats for frogs and dragonflies
○ Seasonal changes in wind and temperature drive nutrient cycling in lakes and ponds
○ Eutrophication due to fertilizers on surrounding soil causing algal blooms
①-② Rivers and Streams (Freshwater) : Flowing bodies of water in one direction
○ Upper reaches : Clean and fast-flowing
○ Middle reaches : Warmer, support growth of diverse aquatic life and algae
○ Lower reaches : Flow slowly to the sea, sediment-rich, low light penetration, decreased photosynthesis, increased decomposers, low dissolved oxygen, benthic feeders increase
①-③ Wetlands (Freshwater) : Areas where aquatic plants grow
○ Difference from lakes and ponds : Soil surrounding wetlands contains a lot of water
○ Many species, like tropical rainforests
○ Functions : Slow water flow to control flooding, filter toxins and sediment
○ Over 50% of wetlands in the US have been lost or destroyed
② Marine Ecosystems : Humans have altered 50% of Earth’s surface
① Energy and Natural Resources
○ Energy use (e.g., fossil fuels) : Importing energy resources results in environmental degradation
○ Natural Resources : Require a lot of natural materials for sustenance like food, housing, water
○ Ecological Footprint : Land area needed to support human activities is much larger than actual area
② Waste Production
○ Water Pollution : Factories release solid waste as sludge, chemicals as industrial wastewater → Advanced countries have better sewage treatment
○ Waste : Most solid waste ends up in landfills (in developed countries) or open areas (in developing countries)
③ Air Pollution
○ Primary Pollutants : Emitted from burning fossil fuels like coal and oil
○ CO2, CH4 : Absorb infrared, causing the greenhouse effect
○ SO2, SO3 : Dissolve in water to form acid rain; indicator species is lichen
○ N2O, NO, NO2 : Acid rain or secondary pollutants
○ Hydrocarbons : Secondary pollutants; harmful to eyes and respiratory system
○ CFCs : Ozone layer depletion
○ Particulate matter
○ Secondary Pollutants : Formed by sunlight acting on primary pollutants
○ Ozone, Formaldehyde, PAN : Cause respiratory diseases
○ Smog :
Formed by formaldehyde, PAN, SO2
④ Water Pollution
○ Dissolved Oxygen (DO)
○ Biological Oxygen Demand (BOD)
○ Chemical Oxygen Demand (COD)
⑤ Soil Pollution, Biomagnification
○ Acidification of soil due to chemical fertilizers, pesticides, etc.
○ Mercury (Minamata disease), Cadmium (Itai-itai disease)
Input: 2020.10.25 19:34