Introduction: Let's Learn About the "Connections" That Support Our World
Hello! How is your "Biology" study going? You might be worried that "there's so much to memorize," but don't worry. The topic we’re covering today, "Biodiversity and Ecosystems," is a dynamic and fascinating field that explores how the nature around us is constructed.
This chapter appears frequently on major exams, but if you understand the underlying mechanisms—the "why" behind things—rather than just memorizing facts, your scores will improve dramatically. Relax, imagine a forest or park nearby, and let's dive in!
1. Vegetation and Succession
The collection of plants growing in a certain area is called vegetation. The general appearance of an area (what we call physiognomy), such as a forest, grassland, or wasteland, is determined by the dominant species (the most prominent plants found there).
(1) Plant Succession
The process of change where plants gradually inhabit a bare area over many years, eventually leading to a stable forest, is called succession (which reaches a climax).
【Steps of Xerarch Succession】
1. Bare land/Wasteland: A place with no soil or nutrients. A few lichens or mosses begin to appear.
2. Grassland: Grasses like Japanese silver grass grow, and soil begins to form.
3. Shrubland: Short, sun-loving trees (shade-intolerant shrubs) start growing.
4. Sun-tree forest: Sun trees (trees that require plenty of sunlight, like pines or birches) grow large.
5. Mixed forest: Under the shade of the sun trees, shade trees (like evergreen oaks) that can grow in low light begin to emerge.
6. Shade-tree forest (Climax): The forest floor becomes too dark for sun-tree seedlings to grow. As a result, the area becomes a stable forest consisting entirely of shade trees.
Key Point: Remember, "It starts with sun-loving trees and ends with shade-tolerant trees!"
Fun Fact: Succession that starts in an area where soil already exists, such as after a forest fire, is called secondary succession. Because the soil is already present, the starting phase is much faster.
★ Common Mistake:
The idea that "The climax is a sun-tree forest" is incorrect. Sun trees cannot grow their own offspring in the shade they create, so the forest eventually transitions to shade trees.
2. Climate and Biomes
The reason some places are "tropical rainforests" while others are "deserts" is due to differences in temperature and precipitation. The collection of organisms adapted to these environments is called a biome.
(1) Japanese Biomes (Horizontal Distribution)
Because Japan stretches north to south, biomes change based on temperature.
・Warm-temperate zone (e.g., Western Japan): Laurel forest (Evergreen broad-leaved trees like chinquapin, oak, and camphor). Characterized by glossy, shiny leaves.
・Cool-temperate zone (e.g., Eastern Japan): Deciduous broad-leaved forest (Beech, Japanese oak). These trees shed their leaves in winter.
・Subarctic zone (e.g., Hokkaido): Coniferous forest (Yezo spruce, Sakhalin fir). Characterized by needle-like leaves.
(2) Japanese Biomes (Vertical Distribution)
As you climb a high mountain, the temperature drops, causing the biomes to change (higher altitude ≒ moving north).
・Hill zone (foothills)
・Mountain zone (e.g., Beech)
・Subalpine zone (e.g., Veitch's fir, Northern Japanese hemlock)
・Alpine zone (e.g., Siberian dwarf pine, alpine plants)
※ The boundary altitude where forests can no longer grow is called the timberline (around 2,500m above sea level).
Summary: For biome questions, the shortcut to passing is being able to read graphs with "Temperature (vertical axis)" and "Precipitation (horizontal axis)"!
3. Ecosystem Structure and Material Cycling
The community of organisms in a certain region and their surrounding environment together are called an ecosystem.
(1) Components of an Ecosystem
・Abiotic environment: Light, water, air, temperature, soil, etc.
・Biotic environment:
1. Producers: Perform photosynthesis to create organic matter (plants, plankton).
2. Consumers: Eat other organisms (herbivores, carnivores).
3. Decomposers: Break down remains and waste (fungi, bacteria).
Action and Reaction:
The influence the environment has on organisms is called action (e.g., light allows plants to grow), while the influence organisms have on the environment is called environmental formation (reaction) (e.g., forests help maintain humidity).
(2) Energy Flow
Within an ecosystem, matter "cycles," but energy flows in a "one-way street" and does not cycle. Ultimately, energy escapes as heat.
Relationship between production and consumption (It looks like a formula, but it’s just common sense!):
\( \text{Net Production} = \text{Gross Production} - \text{Respiration} \)
\( \text{Growth} = \text{Net Production} - (\text{Consumption by predators} + \text{Death}) \)
※ This might seem difficult at first, but it's easy to understand if you think: "The remaining money after subtracting living expenses (respiration) from your salary (gross production) becomes your savings (net production)."
Key Point: The higher up in the food chain you go, the less usable energy is available. That is why there are far fewer lions than zebras.
4. Ecosystem Balance and Conservation
Ecosystems have the power to return to their original state even after some changes (self-purification and resilience). However, when human activity exceeds these limits, the balance is disrupted.
(1) Three Levels of Biodiversity
1. Genetic diversity: Even within the same species, individual organisms have slightly different genes.
2. Species diversity: The existence of various types of organisms.
3. Ecosystem diversity: The existence of various environments, such as forests, rivers, and wetlands.
(2) Human Impact
・Invasive species: Organisms introduced to places where they did not originally exist. They cause disruption to ecosystems.
・Eutrophication: An excess of nutrients in water caused by sewage, etc., leading to massive blooms of plankton (e.g., red tides).
Conclusion: Summary of This Chapter
・Succession starts with sun-loving trees and stabilizes with shade-tolerant trees (climax).
・Biomes are determined by temperature and precipitation; in Japan, laurel forests, deciduous broad-leaved forests, and coniferous forests are crucial.
・In an ecosystem, matter cycles, while energy flows in a one-way street.
・Biodiversity exists at three levels: genetic, species, and ecosystem.
This field of "Basic Biology" is directly connected to our daily lives. When you see news about environmental issues, try to recall, "Oh, this is the biome topic I studied in class!" Understanding will deepen significantly. You've got this!