Ecosystems and Evolution Notes

Reproductive Isolation and Differential Selection

  • Speciation Requires Two Processes:
    1. Reproductive Isolation:
      • Populations must cease interbreeding to split into separate species.
      • Interbreeding mixes genes, blending traits, while speciation requires separation and divergence.
      • The genes of a population are termed a gene pool.
      • Speciation necessitates barriers to prevent gene flow between gene pools, achievable through reproductive isolation methods.
    2. Differential Selection:
      • Natural selection changes population traits; similar selection in two populations maintains trait similarity, preventing speciation.
      • Differences in selection cause gradual divergence in traits.
      • Factors contributing to differential selection:
        • Climate (temperatures, rainfall).
        • Predation (different predators or absence thereof).
        • Competition (varying resource competition).
  • Taxonomists classify significantly diverged populations as separate species.

Bonobos and Chimpanzees: An Example of Speciation

  • Bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) are closely related but geographically separated by the Congo River.
  • Neither species can swim, preventing gene flow.
  • Hypothesis:
    • Historically, lower water levels allowed chimpanzees to cross the river.
    • Subsequent rise in water levels geographically isolated migrants.
    • The founder population faced different selection pressures, including abundant food.
    • This divergence led to the evolution of bonobos from chimpanzees.

Types of Biodiversity

*   Biodiversity: The variety of life in all its forms, levels, and combinations.
    *   Ecosystem Diversity: Variety in species combinations within communities, influenced by varied environments and geographical ranges.
    *   Species Diversity: Many different species on the evolutionary tree of life, with varied body plans, internal structure, life cycles, and modes of nutrition.
    *   Genetic Diversity within Species: Variety in the gene pool of each species, with variation between geographically separated and within populations.

Anthropogenic Causes of the Sixth Mass Extinction

  • A sixth mass extinction is underway, caused by human activities (anthropogenic).
  • Case Studies of Extinction:
    1. Caribbean Monk Seal:
      • Neomonachus tropicalis native to the Caribbean Sea and western Atlantic.
      • Hunted for oil in the 18th and 19th centuries.
      • Easy target due to beach breeding, slow movement, and lack of fear of humans.
      • Overfishing of coral reefs led to starvation.
    2. Giant Moa:
      • Dinomis novaezealandiae, native to New Zealand.
      • Height up to 3.6m and mass of 230 kg.
      • Extinction within 200 years of human settlement (Māori iwi) due to hunting for meat.
    3. Silphium:
      • Plant from Libya, extinct within a few hundred years of ancient Greek arrival.
      • Harvested for birth control.
      • Overgrazing and desertification may have contributed.
    • Overharvesting was the main cause of extinction in these three case studies.
  • Other Common Causes of Extinction:
    • Habitat destruction:
      • Natural habitats destroyed, mainly due to agriculture.
      • Over 13 billion hectares of land cultivated or used for livestock.
      • Also destroyed for towns and cities.
    • Invasive Species:
      • Alien species drive native species to extinction through:
        • Predation.
        • Spreading pests and diseases.
        • Competition for resources.
      • Endemic species extinct if hybridize with alien species.
    • Pollution:
      • Chemical industries produce pollutants.
      • Burning fossil fuels, agriculture, mining, oil extraction, and pharmaceuticals are major pollution sources.
    • Global Climate Change:
      • Human activities rapidly changing temperature, rainfall, and other climatic variables.
      • Species unable to adapt or migrate face extinction.

Ecosystem Loss

  • Ecosystem replacement due to environmental changes is natural over long periods like glacial-interglacial cycles (past 2.6 million years).
  • However, recent ecosystem loss is unprecedentedly rapid and anthropogenic.
  • Examples of ecosystem loss:
    1. Mixed Dipterocarp Forest (MDF) of Southeast Asia
      • Dipterocarps are tropical hardwood trees.
      • MDF has high tree species diversity, especially on nutrient-poor sandy soils.
      • Widely logged (legally and illegally) for merchantable timber since the 1970s.
      • Losses greatest on lowland sites with nutrient-rich soils over deep peat.
      • Land conversion to palm oil plantations is a major cause of loss.
      • Peat, up to 15 m deep, stores 250 tonnes of carbon/hectare.
      • Drainage causes peat decomposition, releasing CO_2.
      • Rising sea levels from global warming will flood remaining MDF.
    2. Loss of the Aral Sea
      • Between Kazakhstan and Uzbekistan, was the fourth largest lake in the world.
      • Rivers fed it, but no outflows, so water removed by evaporation.
      • Salinity higher than freshwater lakes.
      • In the 1960s, a water management scheme diverted rivers to irrigate the desert.
      • This led to falling water levels and desertification.
      • Increased salinity (from 1\% to over 22\%) caused ecosystem collapse.
      • All 24 endemic fish species are now extinct.

Causes of Ecosystem Loss

  • Agriculture: main cause of ecosystem loss, with temperate forests/grasslands cleared before the 1970s and tropical forests since then.
  • Urbanization: Building homes, offices, factories, and infrastructure due to rapid population growth.
  • Overexploitation: Gathering fuel wood, hunting, and fishing; loss of keystone species threatens ecosystems.
    *Overfishing on the Canadian Grand Banks is explored in Section D4.2.6.
  • Mining and Smelting: Opencast mines destroy ecosystems; smelting and waste disposal cause pollution. Much tropical rainforest lost due to mining.
  • Water Management: Reservoirs flood ecosystems; water extraction reduces river flows.
  • Drying of Wetlands: Swamps drained for agriculture; water diverted for human use.
    *This is explored for HL in Section D4.2.15.
  • Leaching: Fertilizers washed into rivers/lakes cause eutrophication, loss of oligotrophic ecosystems.
    *This is explored in Section D4.2.8.
  • Climate Change: Anthropogenic climate change is the most common cause of loss. Relationships between ecosystem types and climate are further explored in Theme B and the likely future effects of climate change are considered in Theme D.

The Biodiversity Crisis

  • Species extinction is natural but current rates are 100-1,000 times higher than normal and rising.
  • A biodiversity crisis has been developing since about 1970.
  • Causes:
    • Hunting and over-exploitation.
    • Urbanization.
    • Deforestation and habitat loss.
    • Pollution.
    • Alien invasive species.
  • Humans have been causing species extinctions for thousands of years, but the intensity has increased greatly in the last 100 years.
    *This is a consequence of the enormous rise in the number of people on Earth.
    *Between 1920 and 2020 the human population more than quadrupled, from less than two billion to almost eight billion.
    *Overpopulation is the overarching issue that makes human activities a threat to most other species and risks widespread ecosystem.collapse.

Conservation of Biodiversity

  • No single approach is sufficient; measures must be tailored to species/ecosystems and the causes of loss.
  • In situ conservation: species remain in natural habitats.
    • Ideally, large pristine wilderness areas; partially degraded areas can become nature reserves/national parks.
    • Species live in adapted abiotic environments, interacting with wild species, maintaining ecological niches.
    • Requires management: removal of alien species, reintroduction of extinct species, population control, access control, poaching prevention.
  • Rewilding is the return of degraded ecosystems to as natural a state as possible;recovery can be remarkably rapid and balance is then maintained by natural ecological processes instead of human intervention.
  • Ex situ conservation: preservation outside natural habitats.
    • Removal of individuals from the wild.
    • Traditionally, plants in botanic gardens, animals in zoos, aiming for captive-bred release in native habitats.
    • Ecosanctuaries on islands/fenced areas with semi-natural conditions but predator control.
  • Germ plasm storage: long-term storage of living material for future propagation.
    • Seeds in seed banks at low temperatures (around -20°C).
    • Animal germ plasm (tissue, eggs, sperm) in tissue banks at -20 to -200°C.

EDGE of Existence Programme

  • Uses two criteria to identify animal species most deserving of conservation:
    • Evolutionarily Distinct: Few or no close relatives (member of a small clade).
    • Globally Endangered: Likely to become extinct due to threats to remaining populations.
  • Species fitting both criteria (EDGE species) are targeted for intense conservation efforts.
  • Prioritizing species for conservation has ethical, environmental, political, social, cultural, and economic consequences.
  • Scientists have an obligation to ensure that such issues are debated. The preparation of lists of EDGE species is part of the debate.

Adaptation to the Environment

  • Habitats: The Place Where an Organism Lives
  • Description of geographical location, ecosystem type, and physical and chemical conditions.
  • Usually refers to one species but can be described for populations or whole communities.
  • Abiotic Factors Affecting Species Distribution
  • Plant Distribution: Temperature, water availability, light intensity, soil pH, soil salinity, mineral nutrients.
  • Animal Distribution: Water availability, temperature.
    • Species Adaptations and Tolerance
    • Species have ranges of tolerance for abiotic variables.
    • Adaptations suit species for specific physical environments.
  • Organisms are Adapted to their Abiotic Environment
  • Environment: Everything surrounding an organism, including living (biotic) and non-living (abiotic) factors.
  • Adaptations of Grasses to Sand Dunes
  • Challenge: Sand accumulation, high salt concentration, water conservation.
  • Adaptations: Rhizomes, sclerenchyma tissue, fructans, thick waxy cuticle, stomata in hairy furrows.
  • Adaptations of Trees to Mangrove Swamps
  • Challenges: Waterlogged anaerobic soils, high salt concentrations.
  • Adaptations: Salt glands, large buoyant seeds, stilt roots, cable roots, pneumatophores, suberin coating, mineral ions, and carbon compounds.

Range of Tolerance and Limiting Factors

  • Plant and animal species have tolerance ranges for abiotic variables.
  • A limiting factor prevents growth if its level is outside the tolerance range.
  • Transects can be used to Investigate Tolerance Ranges
  • Measurements of abiotic variables and species distribution are needed.
  • Methods include line intercept sampling, belt transects, and observational transects.
  • Formation of Coral Reef
  • Conditions for hard corals:
    * Depth-water less than 50 m, so enough light penetrates.
    * pH-above 7.8 so CaCO, can be deposited in the skeleton.
    * Salinity between 32 and 42 parts per thousand of dissolved ions to avoid osmotic problems.
    * Clarity-turbidity would prevent penetration of light so the water must be clear.
    * Temperature-23-29°C so both the coral and its zooxanthellae remain healthy.

Terrestrial Biome Distribution

  • Ecosystems are determined by abiotic factors.
  • Biomes are ecosystems of a specific type (e.g., taiga).
  • Temperature and rainfall are key determinants of biome distribution on Earth.

Adaptations to Life in Hot Deserts and Tropical Rainforests

  • Hot Deserts
    * saguaro cactus (Camegia gigantea)
    * wide-spreading roots
    * tap roots
    * wide stems with water storage tissue
    * pleated stems that shrink in droughts and swell after rain
    * vertical stems
    * thick waxy cuticle on stem epidermis
    * leaves reduced to spines
    * CAM metabolism
    * fennec fox (Vulpes zerda)
    * nocturnal
    * builds an underground den
    * long thick hair
    * hairs cover the pads of the feet
    * pale-coloured coat reflects sunlight
    * large ears radiate heat
    * ventilation rate rises very high (panting) to cause
    heat loss by evaporation.
    *Tropical rainforest
    * yellow meranti (Shorea faguetiana)
    *grows to over 100 m tall so avoids competition for light
    *trunk of hard dense wood for support against wind stress
    *trunk buttressed at base for support in shallow soil
    *smooth trunk to shed rainwater rapidly
    * oval leaves with pointed tips to shed rainwater rapidly
    *evergreen leaves to carry out photosynthesis all year
    * leaf enzymes work in temperatures as high as 35°C
    * flowers and seeds produced in large quantities
    only about one year in five, to deter animals that eat the seeds.
    *spider monkey(Ateles geoffroyi
    *long arms and legs for climbing and reaching
    *flexible shoulders allowing swinging from tree to tree
    * large hook-like thumbless hands to grasp branches
    and lianas (woody vines) and pick fruit
    *feet can grasp branches so arms can be used
    for feeding
    *long tail to grip branches
    *highly developed larynx for communication in the
    dense rainforest canopy
    *only awake in the daytime-vision is better so
    *movement between branches is safer

*breeding in any season, as food always available.

The Ecological Niche

  • Ecological Niche:
    • Each species has a unique role in an ecosystem.
    • Includes both biotic and abiotic elements.
  • Abiotic elements:
    • Zones of tolerance determine habitat.
  • Biotic Elements:
    • Food supply (autotrophic or heterotrophic).
    • Specialization in sourcing food to minimize competition.
  • Many factors make up the ecological niche.

Oxygen Requirements of Organisms

  • Organisms categorized by oxygen requirements:
    • Obligate Aerobes: Require continuous oxygen for aerobic respiration. Examples: plants and animals.
    • Obligate Anaerobes: Require anoxic conditions, oxygen kills or inhibits. Examples: Clostridium tetani, methanogenic archaea.
    • Facultative Anaerobes: Tolerate anoxic conditions, use oxygen if available. Examples: Escherichia coli, Saccharomyces.

Sources of Carbon

  • Photosynthesis: Energy from sunlight is used for fixing carbon dioxide and making the carbon compounds.
    • Plants: mosses, ferns, conifers and flowering plants
    • Eukaryotic algae including seaweeds
    • cyanobacteria
  • Holozoic nutrition: whole pieces of food ingested + digested (digestion happens internally)
    1. ingestion-taking the food into the gut
    2. digestion-breaking large food molecules into smaller molecules
    3. absorption-transport of digested food across the plasma membrane of epidermis cells and thus into the blood
    and tissues of the body
    4. assimilation using digested foods
    to synthesize proteins and other
    macromolecules; this makes them part
    of the body's tissues
    5. egestion-voiding undigested
    material from the end of the gut.
  • Mixotrophic nutrition:
    • organisms that are not exclusively autotrophic or
      heterotrophic are mixotrophic.
    • Facultative mixotrophs can be autotrophic, heterotrophic, or both.
      *Obligate mixotrophs cannot grow unless they utilize both autotrophic and heterotrophic modes of nutrition.
  • Saprotrophic Nutrition:
    • Saprotrophs feed on dead organic matter and secrete digestive enzymes externally.
    • They secrete proteases to digest proteins into amino acids

Archaea Nutrition

  • Archaea: Diverse nutrition
    *Chemoheterotrophs Oxidation of carbon compounds obtained from other organisms
    *Photoheterotrophs Absorption of light using pigments (notchlorophyll in archaea
    *Chemoautotrophs Oxidation of inorganic chemicals, for exampleFe2+ ions oxidized to Fe³+

Dentition and Diet

*Theories :based on observed patterns or tested hypotheses, that is widely applicable.
*The teeth of herbivores tend to be large and flat to grind down fibrous plant tisuues.
*Omnivores tend to have a mix of different types of teeth to break down both meat and plants in their diet.

Adaptations for feeding and of plants for resisting herbivory

*Animals that feed only on plants are herbivores.
*Insect mouthparts show great diversity, but are all homologous-they have been derived by evolution fromthe same ancestral mouthparts.
*Plants have varied adaptations for deterringherbivore attacks:
*sharp spines (e.g. the thorns of a rose)
*stings to cause pain (e.g. stinging nettle)
*synthesis and storage of secondary metabolites that
are toxic to herbivores

  • herbivores have responded to toxic compounds in plants by developing metabolic adaptations for detoxifying them

Adaptations of Predators and Prey

*Predators adapted to find, catch, kill, and digest prey; prey adapted to resist predation.
*Adaptations:
*Structural
*Chemical
*Behavioural

Fundamental and realized niches

*the range of abiotic conditions tolerated together with the
requirements for biotic factors.
*The actual extent of the potential
range that a species occupies is its realized niche.

Competitive exclusion

*If two species in an ecosystem have overlapping
fundamental niches and one species outcompetes
the other in all parts of the fundamental niche, the
outcompeted species does not have a realized niche
and will be competitively excluded from the whole
ecosystem.
*According to ecological theory, every species
must have a realized niche that differs from the realized
niches of all other species if it is to survive in an ecosystem.

Populations

  • Population: A group of individual organisms of the same species living in an area, interacting with each other.
    • They normally interbreed with each other and interbreed less often or not at all with individuals in other populations
      Random Sampling to Estimate Population Size
      *An estimate in science is not the same as a guess.It should be based on evidence. Estimates of population size are based on sampling.
      *A random sample is one where every member of a
      population has an equal chance of being selected.
      Measurement
      *Measurements are repeated to increase the reliability
      of data
      Estimating Population Size with quadrats
      e.g. if we use the
      coordinates 14.7,
      the quadrat would
      be positioned here
      *
      population mean count per quadratx area of whole site (m²)
      estimate=
      area of one quadrat (m²)

*Standard Deviation of skills Application of skills
*the number of individuals per quadrat in quadrat sampling of
a population.
*The lower the standard deviation, the moreconfidence you can have in any estimates based on thedata

Organisms by Capture-Mark-Release-Recapture Application of skills

*Make Marked-Release-Recapture
*population size/MXN/R

Carrying Capacity

  • Definition: The maximum population size an environment can support.

Density-Dependent Factors

  • Density-Independent Factors: Same effect regardless of population size (e.g., frost killing all plants).
  • Density-Dependent Factors: Increasing effect as population grows (e.g., competition, predation, disease).

Sigmoid Population Growth Curves

  • Factors Contributing to Population Change:
    • Natality (birth rate).
    • Mortality (death rate).
    • Immigration (entering).
    • Emigration (leaving).
  • Phases of Growth:
    • Exponential Phase: Rapid growth in an unlimited environment.
    • Transitional Phase: Growth slows as carrying capacity is reached.
    • Plateau Phase: Population stabilizes due to limited resources.

Modeling Sigmoid Population Growth Curves

*The spread of the collared dove in Europe is aninteresting population growth case study

Communities

*A typicalcommunity consists of hundreds or even thousands
of species, including all the plants, animals, fungi and
bacteria, that live together in an ecosystem
An interspecific relationship is one that exists between individuals of different species.

  1. Competition
    Members of a population have the same ecological
    niche so require the same resources. Unless a resourceis abundant, there will be competition for it. Someindividuals will be more successful and gain more of theresource, helping them to survive and reproduce. As aresult, there is natural selection over the generations fortraits that allow individuals to compete more effectively.
  2. Cooperation
    Individuals in a population may cooperate in a variety ofways. The extent of cooperation varies, with most in socialanimals such as termites.

Categories of interspecific relationship within communities

*Relationships between species not living
in close association Herbivory
Primary consumers feed on producers. The producery.g. bison feeding on grassesay or may not be killed.
*Predation Interspecific competition
Two or more species use the same resource, with theamount taken by one species reducing the amount
*Relationships with close association
Two species live in a close association, with both speciesbenefiting from the association Zooxanthellae in hard corals
*Pathogenicity Parasitism .black-legged ticks on white-tailed deer

Mutualism

Are close associations between species, where both species benefit In many cases, the two species arefrom different taxonomic kingdoms so they have different capabilities and supply different services.
Root nodules in Fabaceae (legumes)
many plants in the and bean familyform a mutualistic relationship withRhizobium bacteriaThe plant grows aroot nodule in which the bacteria canafely liveThe plant provides sugars andlow oxygen environment
Mycorrhizae in orchids (Orchidaceae)
The hyphae of Russula and othermycorrhizal fungi grow into the rootsof orchids and penetrate root cellwalls but not the plasma membrane
Zooxanthellae in hard corals
The zooxanthellae are in a safe environment andand coral in are a safe

Invasive species compete with endemic species

*Species that occur naturally in an area are endemic.
Species that were introduced by humans, deliberately oraccidentally, are alien, If an alien species increases in numberand spreads rapidly, it is invasive.

Investigating Interspecific Competition

  • Approaches:
    • Field Manipulation: Remove one species to see effect on others.
    • Laboratory Experiments: Grow species together and apart.
    • Tests for Association: Random sampling to study co-occurrence.

Application of Chi-Squared Tests

*Are two species foundin the same quadrats, different quadrats or are theyrandomly distributed?
*1. Define the two alternative hypotheses:
H₁: two species are distributed independently(This is the null hypothesis)H₁: two species are associated.

  1. Draw up a contingency table of observedfrequencies (the numbers of quadrats containing andnot containing the species).

Predator-Prey Relationships

  • in predator and prey populations are mostly seen inhabitats where weather conditions vary from year toyear.

Control of Populations in Communities

  • Interactions in food chains for population control.
    • Top-down control: Higher trophic levels control lower ones.
    • Bottom-up control: Lower trophic levels control higher ones.

Antibiotics and Allelopathic Agents

Antibiotics are secreted by microorganisms to kill,
inhibit or prevent the growth of other species ofmicroorganism.
Allelopathic agents are secreted into the soil by plants

to kill or deter the growth of neighboring plants.

Energy and Matter in Ecosystems

  • Ecosystems: Composed of all organisms in an area and their abiotic environment.
  • Types of Systems
    • Open Systems: Resources (chemical substances and energy) can enter and exit.
    • Closed Systems: Energy can enter and exit, but chemical resources cannot.
      *Sunlight sustains most ecosystems
      There are ecosystems where little or
      no light penetrates, for example caves
      and in oceans at depths greater than
      200m. Some energy may pass to these
      ecosystems in dead organic mattertransferred from other ecosystems, whichcan be digested by saprotrophs.

Energy Flow in Ecosystems

  • Food Chain: A sequence of organisms, each feeding on the previous.
    *Chemical energy flows along a food chain from organism to organism Arrows are used to indicate the direction of energy flow.

Food Chains and Food Webs

*Feeding relationships in ecological communities are web-like.
A food web is a modelsummarizes all of the possible food chains in a community
Arrows indicate the direction of transfer ofenergy and Biomass

Decomposers/Waste Disposers and Recyclers of Ecosystems

*Dead organic matter is generated by these processes
death of whole organisms
defecation (removal of faeces from the gut)
shedding of leaves, skin cells, hairs, arthropodexoskeletons (moulting) and other unwanted
body parts.

Decomposers Role

  • Without extracellular digestion carried out by
    decomposers, dead organic matter would build up yearby year. Also ions such as ammonium (,NH4+) would not berelEased into the abiotic environment, so other organismsthat absorb them would lose their supply.

Autotroph/Carbon Source

Rediction reaction inside autotrophic cell converts the simple inorganic carbon sources into an initialcarbon compound. This process is carbon fixation. Requires an External Energy Source

Photoautotrophs and Chemoautotroph's

  • Photoautotrophs use sunlight to make carboncompounds by photosynthesis.
    *Chemoautotrophs use exothermic inorganicchemical reactions.
    Heterotrophs
    *Many organisms obtain carbon compounds from,other organisms They digest carbon