Topic outline

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  Course: plants and environment

  Chapter I: Biocenosis

   Chapter Objectives 

   At the end of this chapter, the student will be able to: Define biocenosis and understand its role in an ecosystem. Identify the main characteristics of biocenoses. Differentiate the types of biocenoses according to various criteria. 

  - 1. Introduction The study of the relationships between plants and their environment relies on understanding ecosystems, which are composed of two major elements: The biotope: the set of physicochemical conditions of an environment. The biocenosis: the community of living beings (plants, animals, microorganisms) that interact within this environment. Biocenosis plays a fundamental role in ecological balance by regulating the flow of energy and nutrients through the different trophic levels (producers, consumers, decomposers).

   -2. Notions of Biocenosis Definition of Biocenosis Biocenosis refers to the set of living organisms coexisting in the same environment and interacting with each other and their surroundings. This concept was introduced by Karl Möbius in 1877 to describe biological communities present in a given habitat. An ecosystem is therefore composed of: A biotope, which represents the physical environment. A biocenosis, which includes living beings and their interactions. 

   -2.1. Characteristics of Biocenoses Biocenoses are defined by several characteristics:

   1. Specific Composition The diversity of species within a biocenosis is essential for its functioning. It includes: Species richness: the total number of species present. Relative abundance: the proportion of each species compared to others.

   2. Trophic Organization Biocenoses are structured into food chains and trophic networks: Primary producers (plants, algae): convert solar energy into organic matter. Consumers (herbivores, carnivores, omnivores): feed on other organisms. Decomposers (bacteria, fungi): recycle organic matter into nutrients usable by plants.

  3. Interactions Between Species Organisms within a biocenosis interact through several types of ecological relationships: Competition: two species use the same limited resource (e.g., competition for light among plants). Predation: one species consumes another (e.g., phytophagous insects). Mutualism: a beneficial relationship for both partners (e.g., mycorrhizae in plants). Parasitism: one organism lives at the expense of another (e.g., parasitic fungi on plants). 

   4. Dynamics and Evolution of Biocenoses Biocenoses are not static; they evolve through processes such as: Ecological succession: the gradual replacement of species within an ecosystem (e.g., recolonization of land after a fire). Ecological resilience: the ability of a biocenosis to recover after a disturbance (e.g., forest regeneration after a storm). 

  - 2.2. Types of Biocenoses Biocenoses can be classified according to several criteria:

   1. Based on the Living Environment Terrestrial biocenosis: includes organisms living on land (forests, savannas, deserts). Aquatic biocenosis: includes communities living in aquatic environments (oceans, rivers, lakes). 

   2. Based on Biodiversity and Stability Stable biocenosis (climax): an ecosystem that has reached maturity with a stable ecological balance (e.g., ancient tropical forests). Unstable biocenosis (pioneer community): a community in formation, often after a disturbance (e.g., vegetation on a newly forming sand dune).

   3. Based on Human Intervention Natural biocenosis: develops without human intervention (e.g., primary forests). Anthropized biocenosis: modified by human activities (e.g., agricultural fields, urban parks). 
  

  • Annonces Forum
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  TD1

  1: Study the main terrestrial biomes (tundra, taiga, desert, steppes, Mediterranean ecosystems).

  2. Identify their climatic, geographical, and vegetative characteristics.

  Study of the main terrestrial biomes:

  Tundra

  • Climatic characteristics: Cold, long and dark winters, short and cool summers.
  • Geographical characteristics: Marshy areas, lakes, and low-fertility soils.
  • Vegetative characteristics: Low and sparse vegetation, dominated by mosses, lichens, and small shrubs such as willows and birches.

  Taiga

  • Climatic characteristics: Cold, long winters, short and cool summers.
  • Geographical characteristics: Boreal forests, acidic soils.
  • Vegetative characteristics: Dominated by coniferous trees such as pines and spruces.

  Desert

  • Climatic characteristics: Arid, hot, with low precipitation.
  • Geographical characteristics: Sandy and rocky landscapes, absence of dense vegetation.
  • Vegetative characteristics: Xerophytic plants adapted to drought, such as cacti.

  Steppes

  • Climatic characteristics: Temperate, cold winters, hot summers.
  • Geographical characteristics: Vast grasslands, fertile soils.
  • Vegetative characteristics: Dominated by herbaceous plants such as grasses and wild cereals.

  Mediterranean Ecosystems

  • Climatic characteristics: Hot summers, mild winters, summer drought.
  • Geographical characteristics: Coastal regions, mountainous areas.
  • Vegetative characteristics: Sclerophyllous forests with trees such as holm oaks and Aleppo pines.

  
  
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  cours suite

  The Main Terrestrial Biomes

  1. Tundra

  The tundra is a cold biome mainly found in Arctic and sub-Arctic regions. It is characterized by:

  • Very low annual average temperatures (barely above 0°C in summer).

  • Deeply frozen soil (permafrost).

  • Low-growing vegetation consisting of mosses, lichens, grasses, and small shrubs.

  • Relatively low biodiversity, but well adapted to extreme conditions.

  • A short growing season (2-3 months).

  2. Boreal Forest (or Taiga)

  The boreal forest is located south of the tundra in northern areas of the Northern Hemisphere:

  • Cold temperatures with long, snowy winters.

  • Dominated by conifers (pines, spruces, firs, larches).

  • Acidic and nutrient-poor soils.

  • Fauna adapted to cold conditions: moose, brown bears, lynx, wolves.

  3. Temperate Deciduous Forest

  This biome is found in temperate zones with four well-defined seasons:

  • Moderate temperatures with regular precipitation.

  • Deciduous trees: oaks, beeches, maples.

  • Rich and fertile soils.

  • High animal and plant biodiversity.

  4. Mediterranean Ecosystems

  Found in Mediterranean regions and also in California, Chile, South Africa, and Australia:

  • Hot, dry summers and mild, wet winters.

  • Vegetation adapted to drought (maquis, garrigue).

  • Predominance of sclerophyllous species (thick and tough leaves).

  • Rich and endemic biodiversity.

  5. Temperate Steppe (American Prairie)

  Characterized by:

  • Low precipitation (250 to 500 mm per year).

  • Grass-dominated vegetation.

  • Very fertile soils (chernozems).

  • Used for intensive agriculture and livestock.

  • Fauna: bison, antelopes, rodents.

  6. Deserts

  Extremely arid biomes characterized by:

  • Very low precipitation (< 250 mm per year).

  • Extreme temperatures (hot during the day, cold at night).

  • Sparse vegetation (cacti, succulents).

  • Adapted fauna: reptiles, nocturnal rodents, insects.

  7. Tropical Savanna

  A transition biome between tropical forest and desert:

  • Moderate rainfall with a prolonged dry season.

  • Vegetation: tall grasses, scattered trees (acacias, baobabs).

  • Highly diverse fauna: elephants, giraffes, lions, antelopes.

  • Human activities: agriculture, extensive livestock farming.

  8. Equatorial Rainforest

  Located around the equator (Amazon, Congo Basin, Southeast Asia):

  • Constant temperatures (±27°C) and very high rainfall (>2000 mm/year).

  • Forest stratification (canopy, understory, forest floor).

  • Lush vegetation with evergreen foliage.

  • Exceptional biodiversity (birds, insects, mammals, plants).

  • Conclusion

  Terrestrial biomes present a wide variety of adaptations to climatic and ecological conditions. Understanding them is essential for biodiversity conservation and sustainable natural resource management.

  
  
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  I.2 – Ecosystems: Classification and Characteristics

  1. Terrestrial Ecosystems Associated with Emerged Continents

  Terrestrial ecosystems develop on continental surfaces and are influenced by climatic, geological, and biological factors. 

    Characteristics:

  - Tropical Forests:  Extreme biodiversity, high temperature, and humidity (e.g., Amazon Rainforest). 

  - Deserts: Low precipitation, vegetation adapted to drought (e.g., Sahara Desert). 

  - Grasslands and Savannas:  Dominated by grasses, marked dry and wet seasons (e.g., Serengeti). 

  - Tundra: Polar climate, frozen soil (permafrost), low vegetation (e.g., Siberia). 

  - Mountains: Altitudinal zonation with variations in temperature and pressure (e.g., Alps). 

  Key Components: 

  - Biotic:  Plants, animals, microorganisms. 

  - Abiotic: Soil, temperature, light, precipitation. 

  2. Aquatic Ecosystems

  Aquatic ecosystems include freshwater and marine environments, structured by depth, salinity, and currents. 

  Types:

  - Freshwater:

    - Lentic(still waters: lakes, ponds). 

    - Lotic (flowing waters: rivers, streams). 

  - Marine:

    - Coastal Zones(mangroves, coral reefs). 

    - Pelagic (open waters, plankton). 

    - Abyssal (dark depths, bioluminescent organisms). 

  Biological Adaptations:

  - Organisms with gill respiration (fish). 

  - Floating plants (water lilies) or fixed plants (algae). 

  3. Microecosystems

  Small-scale ecosystems where biotic and abiotic interactions are localized. 

  Examples: 

  - A puddle of water: Insect larvae, algae, bacteria. 

  - A dead tree trunk: Fungi, beetles, worms. 

  - The gut microbiome: Bacteria, archaea, yeasts. 

  Importance:

  - Maintenance of biodiversity on a small scale. 

  - Natural laboratories for studying ecological interactions. 

  4. Mesoecosystems

  Intermediate-scale ecosystems often corresponding to specific landscapes or habitats. 

  Examples:

  - A temperate forest: Trophic networks including herbivores, carnivores, and decomposers. 

  - A lake: Littoral zones, pelagic zones, and deep zones with distinct communities. 

  - An agricultural field: Interactions between crops, pollinators, and pests. 

  Functions: 

  - Regulation of biogeochemical cycles (C, N, P). 

  - Support for ecosystem services (pollination, water purification). 

  5. Macroecosystems

  Large-scale ecosystems at the planetary or regional level encompassing entire biomes. 

  Examples:

  - Biosphere: Interaction between all Earth's ecosystems. 

  - Biomes: 

    - Boreal Forest(taiga). 

    - Indian Ocean (tropical marine ecosystems). 

    - Great Grasslands (steppes). 

  Challenges: 

  - Climate change and melting polar ice caps. 

  - Deforestation and biodiversity loss. 

  Synthesis and Interactions

  - Ecological Hierarchy: Microecosystems integrate into mesoecosystems and then into macroecosystems. 

  - Resilience: Disturbances (fires, pollution) affect each scale differently. 

  - Conservation:Protecting ecological corridors to maintain connectivity between ecosystems. 

  Applications: 

  - Sustainable resource management (fishing, agriculture). 

  - Ecological restoration (species reintroduction, reforestation). 

  
  

  Citations:

  [1] https://ppl-ai-file-upload.s3.amazonaws.com/web/direct-files/14194965/c05c1f6e-a3d8-4810-9982-e7d37bef1b48/paste.txt

  [2] https://ppl-ai-file-upload.s3.amazonaws.com/web/direct-files/14194965/613bde92-63ae-4c4f-a1c9-79f18e81c51c/paste-2.txt

  [3] https://ppl-ai-file-upload.s3.amazonaws.com/web/direct-files/14194965/4dd5ef25-7aed-49e4-8d9c-e48c96a24d9e/paste-3.txt

  [4] https://ppl-ai-file-upload.s3.amazonaws.com/web/direct-files/14194965/6ad63200-bfe3-401b-9df1-a96179a239b1/paste-4.txt

   

  
  
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  Topic 4

  I.3 Plant Responses to Environmental Factors

  1. General Response Mechanisms
  Plants, as sessile (fixed) organisms, cannot escape unfavorable environmental conditions. Therefore, they have developed physiological, morphological, and behavioral adaptation mechanisms to respond to various environmental factors, including:

  🌱 1. Adaptation

  ➤ Definition:
  Adaptation is a stable and hereditary genetic modification of a plant species that enables it to survive in a given environment. It results from natural selection over long periods of time.

  ➤ Characteristics:

  • Hereditary: Passed on to future generations.

  • Long-term: Part of the evolutionary process.

  • Leads to the emergence of ecotypes or specialized species.

  ➤ Examples:

  • Desert cacti have developed thick stems to store water and spines instead of leaves to reduce evaporation.

  • Alpine plants have rosette-shaped, often hairy leaves to conserve heat and protect against wind.

  ---

  🌿 2. Acclimation

  ➤ Definition:
  Acclimation is a reversible and non-hereditary physiological response to an environmental change. It allows the plant to quickly adjust to a change, but it is not passed on to offspring.

  ➤ Characteristics:

  • Short to medium term (from days to seasons).

  • Depends on the adaptive potential of the species.

  • Helps maintain optimal physiological function.

  ➤ Examples:

  • A plant exposed to more light may produce more photosynthetic pigments (chlorophyll, carotenoids).

  • During temporary drought, some plants close their stomata to reduce water loss (a reversible mechanism).

  ---

  ☀️ 3. Avoidance

  ➤ Definition:
  Avoidance is a set of strategies that allow a plant to reduce or bypass exposure to stress without directly resisting it.

  ➤ Types:

  • Morphological avoidance: Structural changes.

  • Phenological avoidance: Adjustment of the life cycle.

  ➤ Examples:

  • Closing stomata during the hottest hours of the day (to avoid excessive transpiration).

  • Desert annuals: rapid germination and short life cycle limited to the rainy season (avoiding summer drought).

  • Vertically oriented leaves to avoid maximum sun exposure.

  ---

  ❄️ 4. Tolerance

  ➤ Definition:
  Tolerance is the plant's ability to maintain vital functions even under intense or prolonged stress.

  ➤ Characteristics:

  • Based on complex internal mechanisms.

  • Can be physiological (production of protective molecules) or biochemical.

  ➤ Examples:

  • Production of heat shock proteins (HSPs) that protect enzymes at high temperatures.

  • Synthesis of osmoprotectant compounds (proline, sugars) during water or salt stress.

  • Accumulation of antioxidant pigments (flavonoids, anthocyanins) to neutralize free radicals during light or oxidative stress.

  ---

  🧬 Visual Summary of Mechanism | Duration | Nature | Typical Example

  Mechanism	Duration	Nature	Typical Example

  Adaptation

  Long-term

  Genetic

  Cactus spines

  Acclimation

  Short-term

  Physiological

  Stomatal opening

  Avoidance

  Variable

  Morphological or phenological

  Short life cycle in annuals

  Tolerance

  Short or long-term

  Biochemical / Cellular

  Antioxidant synthesis

  
  

  3. Response to Resource Availability

  Plants depend on abiotic resources: light, water, CO₂, and soil nutrients.

  a. Light:

  • Phototropism: Orientation toward light.

  • Photoperiodism: Response to day/night ratio (triggers flowering or dormancy).

  • Leaf acclimation: Adaptation to light intensity (shade vs. sun leaves).

  b. Water:

  • Water-saving mechanisms: Reduced leaves, thick cuticles, sunken stomata.

  • Plant types: Xerophytes, mesophytes, and hydrophytes depending on humidity levels.

  c. Nutrients:

  • Adapted root systems: Deep roots, mycorrhizae.

  • Growth reduction in case of deficiencies.

  ---

  4. Plant Distribution

  The distribution of plant species depends on:

  • Climatic conditions: Temperature, rainfall, sunlight.

  • Soil characteristics: pH, texture, nutrient content.

  • Human activities: Agriculture, deforestation, urbanization.

  👉 This distribution creates biogeographical zones and biomes where only specifically adapted species can survive.

  ---

  🌿 I.4 Functioning of Plant Communities

  1. Spatio-temporal Variations in Plant Communities

  Plant communities evolve over time (ecological succession) and across space (zonation, gradients).

  a. Ecological Succession:

  • Primary: On virgin substrates (lava, dunes).

  • Secondary: After disturbances (fire, abandoned farmland).

  • Leads to climax communities: Stable ecosystems.

  b. Spatial Variability:

  • Depends on microclimates, topography, soil moisture.

  • Zonation in mountains, forests, wetlands, etc.

  ---

  2. Functioning of Communities and Biogeochemical Cycles

  Plant communities play a key role in major natural cycles:

  a. Carbon Cycle:

  • Photosynthesis → CO₂ storage → Primary productivity.

  • Crucial role in climate regulation.

  b. Nitrogen Cycle:

  • Nitrogen fixation by legumes.

  • Nitrate absorption by plants, return through decomposition.

  c. Water Cycle:

  • Transpiration and evapotranspiration.

  • Important for regulating soil and atmospheric moisture.

  ---

  3. Human Impact on Vegetative Cover Functioning

  Human activities drastically alter plant ecosystems:

  • Deforestation: Loss of biodiversity, changes in local climate.

  • Intensive agriculture: Soil depletion, pollution from fertilizers.

  • Urbanization: Fragmentation of natural habitats.

  • Climate change: Shift in species distribution ranges, water stress.

  Consequences:

  • Decline in ecosystem services (carbon storage, water filtration).

  • Loss of ecological resilience.

  • Need for sustainable management and ecological restoration.

  ---

  ✅ Conclusion

  Studying how plants respond to environmental factors helps us understand their distribution, adaptation, and vulnerability to change. The functioning of plant communities is closely tied to natural cycles, biodiversity, and ecological balance. Understanding these interactions is essential for ecosystem conservation and sustainable development.

  
  
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  TD 2

  📝 Exercise 1: Multiple Choice Review 

  Check the correct answer(s).

  The tundra is characterized by:
  ☐ Tropical biodiversity
  ☐ Permafrost
  ☐ Heavy rainfall
  ☐ Low-growing vegetation

  Lentic ecosystems correspond to:
  ☐ Rivers and streams
  ☐ Lakes and ponds
  ☐ Coastal areas
  ☐ Abyssal zones

  An example of a microecosystem is:
  ☐ The Amazon rainforest
  ☐ A puddle of water
  ☐ An alpine meadow
  ☐ A mangrove

  Which of the following is an abiotic factor?
  ☐ Fungus
   ☐Temperature
  ☐ Insect
  ☐Precipitation

  An example of plant adaptation in desert environments is:
   Leaves modified into spines
  ☐ Very short roots
  ☐ Dense foliage
   ☐A thick cuticle

  ---

  🧠 Exercise 2: Match each ecosystem with its main characteristic 

  Ecosystem	Main Characteristic
  1. Tropical forest	C. Broadleaf trees, constant humidity
  2. Steppe	B. Dominated by grasses, moderate precipitation
  3. Abyssal ecosystem	A. Extreme environment, great depth, luminous organisms
  4. Stream (lotic ecosystem)	D. Flowing water, rich in oxygen
  5. Intestinal microecosystem	E. Symbiotic microorganisms inside a human host

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  🧩 Exercise 3: Complete the Table 

  Ecosystem Type	Example 🌍/🌊/🔬/🏞️/🌐	Typical Biological Adaptations
  Terrestrial	🌍 ……………………………	…………………………………………………………………………
  Aquatic (lentic)	🌊 ……………………………	…………………………………………………………………………
  Aquatic (lotic)	🌊 ……………………………	…………………………………………………………………………
  Microecosystem	🔬 ……………………………	…………………………………………………………………………
  Mesoecosystem	🏞️ ……………………………	…………………………………………………………………………
  Macroecosystem	🌐 ……………………………	…………………………………………………………………………