Biotic relationships in a mixed forest ecosystem
Biotic factors are forms of interaction between living organisms. These include competition, symbiosis (mutualism), commensalism, neutralism, predation, and parasitism. When analyzing a mixed forest ecosystem involving birch, pine, hawk, birch bolete (Leccinum scabrum), and tinder fungus, the following relationships can be identified:
- Birch and pine — competition, since both species require similar abiotic resources: light, moisture, and soil minerals.
- Birch and hawk — neutralism: the hawk as a predator feeds on small vertebrates and has no direct effect on the tree.
- Birch and birch bolete — symbiosis (mycorrhiza): the fungus receives organic compounds produced during photosynthesis from the plant, while the tree receives water and mineral compounds released from the breakdown of organic matter from the fungus.
- Birch and tinder fungus — parasitism: the tinder fungus absorbs organic substances from the tree tissues, destroys the wood, and harms the plant.
Causes of insect population explosions
A sharp increase in population size (outbreak) occurs when several environmental factors combine:
- an increase in available food resources (feed base);
- favorable climatic (abiotic) conditions — optimal temperature and humidity;
- weakening of intraspecific and interspecific competition;
- decrease in the number of natural enemies — predators and parasites;
- absence of epizootics caused by pathogenic microorganisms.
Biotic links in a freshwater body
In a freshwater body involving swan mussels, crucian carp, pike, and perch, several types of biotic relationships occur simultaneously:
- Predation: pike and perch feed on crucian carp, and adult predatory fish consume juveniles.
- Parasitism: swan mussel larvae (glochidia) attach to the gills and skin of fish, leading a temporary parasitic lifestyle.
- Neutralism: adult swan mussels, leading a benthic filter-feeding lifestyle, do not directly interact with adult fish.
- Competition: pike and perch compete for shared food resources — small fish.
Animal adaptations to the habitat
Morphological and physiological adaptations ensure the survival of a species in specific conditions. Regarding animals in cold and aquatic biotypes, the following are distinguished:
- sebum lubrication of the fur — softens the skin and prevents the coat from getting wet;
- dark coloration — absorbs solar heat, aiding in thermoregulation;
- subcutaneous fat layer — performs thermal insulation and energy storage functions;
- thick fur on the soles of the feet — prevents slipping on ice and snow, reduces heat loss;
- reduced sizes of pinnae and extremities — reduce heat transfer (Allen's rule).
Impact of toxic chemicals on trophic levels
The use of pesticides in agriculture affects various links in food chains:
- Herbicides affect the first trophic level — producers, destroying weed plants.
- Insecticides affect the second and subsequent levels — phytophagous insects, and through bioaccumulation, insectivorous and predatory animals.
- The consequence is a decrease in the numbers of insects and the vertebrates that feed on them, disruption of food chains, and a reduction in agrocenosis biodiversity.
- The accumulation of poisons along the food chain (biomagnification) leads to maximum concentrations of toxicants in higher-order consumers.
Key points
- Biotic factors describe interactions between living organisms: competition, symbiosis, parasitism, predation, neutralism, commensalism.
- Competition arises when species have similar needs for environmental resources.
- The mycorrhiza of birch and birch bolete is a classic example of mutually beneficial symbiosis.
- Population explosions are driven by growth in the food base, favorable climate, and the weakening of biotic resistance.
- Different types of biotic relationships can simultaneously exist between the same species at various stages of ontogenesis.
- Adaptations to cold include thermal insulation, reduction of protruding body parts, and behavioral responses.
- Herbicides affect producers, while insecticides affect consumers at multiple levels.
- Bioaccumulation of toxic chemicals intensifies as it moves up the trophic chain.