Organisms and Population
The chapter on organisms and populations has the key concepts as to how organisms interact with their environment and how the populations grow and deviate from each other. This chapter describes the effects of abiotic factors such as temperature, water, light, and soil on living organisms and the adaptations that allow them survive under different environmental conditions.
This Story also Contains
- Major Abiotic Factors Affecting Organisms and Populations
- Responses to Abiotic Factors
- Adaptations
- Population Attributes
- Population Regulation
- Recommended Video on Organisms and Populations
The chapter also introduces topics such as population dynamics, which have features covering population size, density, birth rate, and death rate. There are various models, such as logistic growth (dN/dt = rN[(K–N)/K]), which help explain the population stabilisation over time. Gause’s competition experiments and mutualism between clownfish and sea anemones are real-life examples that help explain ecological relationships clearly. The chapter forms a base for advanced studies in Biology like ecology, conservation biology, etc.
Important Topics of Chapter: Organisms and Population
- Population Interactions: These are relations among species within a community, e.g., mutualism, predation, competition, parasitism, and commensalism, that affect reproduction and survival.
- Population Attributes: Traits such as population size, density, age distribution, birth rate, and mortality rate that shape the dynamics and structure of a population over time.
- Ecology: The scientific analysis of relations among organisms and between organisms and their physical environment, serving as the foundation for ecosystem processes.
- Biotic and Abiotic Factors: Biotic factors consist of living elements (plants, animals, microbes), while abiotic factors consist of non-living elements (temperature, water, light, soil) that affect an organism's survival and distribution.
- Population Growth Models: Exponential and Logistic Growth
Major Abiotic Factors Affecting Organisms and Populations
Abiotic factors are key factors that form the environment and influence the survival, distribution, and adaptation of organisms. Major abiotic factors include temperature, water, light, and soil, each having unique impacts on living organisms:
Temperature
- Usually closely associated with metabolic and physiological processes in organisms, Enzyme activity changes with temperature.
- Temperature varies widely around the globe: at times less than 0°C in the polar regions, or more than 50°C in deserts.
- Eurythermal organisms (Tilapia, carp, cockroach) can tolerate wide ranges of temperatures, whereas stenothermal organisms (Trout, Antarctic fishes, corals) exist within very narrow temperature ranges.
Water
- Required by all forms of life, fewer species exist in drier areas with low levels of water, like deserts.
- Water availability and its quality (salinity and pH) influence the distribution, survival, and reproduction of organisms.
- Euryhaline species (such as crabs and mollies) tolerate varying salt concentrations, and stenohaline species (like haddock and goldfish) exist only in a small range of salt concentrations.
Light
- Important for the photosynthesis in autotrophs; the sun is the primary source of light.
- Variation in the level of requirement among the organisms leads to changes in the growth patterns of plants and migratory behaviours in animals to reproduce.
- Levels of solar radiation, especially ultraviolet radiation, impact the health and condition of organisms primarily depending on the depth of the ocean.
Soil
- Hence, soil type influences biodiversity but is rather determined by climatic factors, topography, and sedimentation processes.
- Features such as pH, minerals and texture determine the species of plants and animals which survive in a habitat.
- Collectively, these abiotic factors form an ecosystem, determining what's there, how abundant it is and in what adaptations the organisms exist.
Responses to Abiotic Factors
All organisms have different adjustments to withstand various abiotic factors within the environment. Organisms respond to abiotic factors like temperature, light, water, and soil by developing specific survival strategies. The reactions help them survive and live under changing conditions. The major responses include regulation, conformity, migration, and suspension
Regulators
- In this process, a stable internal environment is maintained irrespective of what happens outside.
- Universally present among birds and mammals and some vertebrates, and invertebrates.
- For example, human beings maintain a constant body temperature at 37°C by sweating during hot weather and shivering in cold weather.
Conformers
- Regulate their internal body temperature according to external temperatures and often lack complex thermoregulation.
- Small animals, because of their high surface-to-volume ratio, lose heat rapidly and consequently are not usually found in polar regions.
Migration
- Seasonal movement of animals to avoid tough environmental conditions.
- For instance, many birds migrate from Siberia to Keoladeo National Park in Rajasthan during winter.
Dormancy and Spore Formation
- Spores are formed by certain microorganisms, like bacteria and fungi, to survive hostile environmental conditions.
- Some animals go into dormancy during winter or aestivate when it gets very hot and dry.
Adaptations
Adaptations are inherited structural, physiological, or behavioural characteristics that improve an organism's chances of survival and reproduction in a particular habitat. These can be physiological,i.e., the ability of desert plants to store water. These adaptations are acquired over generations and help the organisms cope with the environment. Some of the most significant are:
Desert Plant Adaptations
- Opuntia and other desert plants have thick stems, spiny leaves, and sunken stomata to minimise water loss.
- These plants adopt CAM photosynthesis at arid temperatures to ensure survival.
Human High-Altitude Adaptations
- People travelling to high altitudes may experience altitude sickness because of low oxygen availability. Over time, the body adapts by increasing red blood cell production and breathing rate.
Behavioural Adjustments
- Some animals have developed certain habits based on particular environmental factors, such as migrating or hibernating.
Population Attributes
The population has specific features that make it different from the individual organism or the whole species. Population attributes refer to the characteristics of a population, such as size, birth rate, death rate, age distribution, and sex ratio, which help in understanding how populations grow and change over time. Among the Organisms and Population Attributes, the following can be described:
Birth And Death Rates
Birth Rate
The number of live births per 1,000 individuals in a population per year.
It shows the reproductive capacity and growth potential of the population.
Death Rate
The number of deaths per 1,000 individuals in a population per year.
It reflects the mortality rate and the general health condition of the population.
Sex Ratio
The ratio of males to females in a population.
Affects mating patterns, reproductive rates and social structure.
This may affect the population growth and dynamics.
Age Distribution
Proportion of individuals in different age groups.
Usually divided into pre-reproductive, reproductive and post-reproductive.
Affects the growth rate of the population and future reproduction potential.
Indicates dependency ratio with implications for economic and social support systems.
Population Density
Number of individuals per unit area/volume.
High densities can lead to increased competition for resources, elevated disease transmission, and social interaction, while low densities may mean difficulties finding mates and increased vulnerability to environmental changes.
Population Growth
The size of the population of any species may never stop, depending on the availability of food sources, weather conditions, and predators. There are four main reasons for the change in population density:
(i)Natality: Number of individuals added to the population through birth.
(ii) Mortality: Number of individuals removed from the population through death.
(iii) Immigration: Number of individuals entering a population from another area.
(iv)Emigration: Number of individuals leaving a population for another area.
If the population density at time t is Nt, then the population density at time t + 1 is represented as:
Nt+1 = Nt + [(B + I) − (D + E)]
Population Growth Models
Exponential Growth
Occurs when resources are unlimited.
Growth follows a J-shaped curve.
Equation: dN/dt = rN
Logistic Growth
Occurs when resources become limited.
The population stabilises around the carrying capacity (K).
S-shaped growth curve.
Equation:
dN/dt = rN[(K−N)/K]
Population Interactions
Population interactions between different organisms can be divided into two categories, namely, interspecific interactions and intraspecific interactions. When an interaction occurs between similar species, then it is called an Intraspecific interaction, while an interaction between different organisms is called an interspecific interaction.
(i) Predation:
- Predation is an interaction in which one organism kills and feeds on another organism.
- Herbivores are also considered predators because they feed on living plants. Plants have evolved defensive adaptations such as thorns and chemicals like nicotine, caffeine, quinine, and latex to reduce herbivory.
(ii) Competition:
- An interaction between organisms in which both organisms compete for a variety of resources, including food, water, habitat, etc. This interaction occurs when resources are limited.
- According to Gause's Competitive Exclusion Principle, two species competing for the same limiting resource cannot coexist indefinitely. One species eventually outcompetes the other.
(iii) Parasitism:
- An interaction where one type is dependent on another type, which leads to the benefit of one type and harms another. Those parasites feed on the outer surface of living organisms, called ectoparasites.
- For example, marine fish include ectoparasitic copepods. In the case of birds, there is Brood parasitism where birds lay their eggs in the host bird's nest while the host incubates them.
(iv) Commensalism:
- An interdependence of species where it is recognised that one species benefits and the other is neither benefited nor harmed.
- For example, an orchid grows like an epiphyte on a mango branch.
(v) Mutualism:
- An interaction where both species benefit from each other.
- Examples are lichens (the relationship between algae and fungi) and mycorrhiza (the symbiotic relationship between fungi and higher plant roots).
(vi) Amensalism:
- An interaction between an organism in which one species is harmed, while the other remains unaffected.
- Example- Production of penicillin by the Penicillium fungus, which inhibits the growth of bacteria without benefiting or harming the fungus itself.
Population Regulation
Population regulation refers to how the size of a population is controlled over time. It depends on factors like food availability, predation, diseases, and competition. Population regulation prevents size and growth in the process of keeping the ecosystem stable. Certain factors affecting the population are:
Density Dependent Factors
- These factors, for example, diseases, predation, and competition, increase as the population density increases.
- For instance, diseases spread fast in dense populations, and competition may limit growth and reproduction.
Density Independent Factors
- These factors, such as natural disasters and climate change, occur regardless of the population's density.
- Hurricanes or shifting of the climate affected polar bears, resulting in a sudden decline in their population.
Human Impact on Populations
- Human factors affect populations through habitat destruction due to paving and pollution, leading to a loss of biodiversity.
- Significant conservation measures include protected areas, the use of renewable resources, and wildlife legislation.
- Other major human impacts include overexploitation of natural resources and the introduction of invasive alien species, both of which reduce biodiversity and disturb ecological balance.
Endangered Species
- Loss of habitats, hunting, global warming, and pollution are the reasons which drive species to extinction.
- Conservation measures involve the creation of reserves, anti-poaching legislation, captive breeding, and habitat restoration.
Recommended Video on Organisms and Populations
Frequently Asked Questions (FAQs)
Any quality of an organism that allows it to live and reproduce in its own place is called adaptation. It is a fixed attribute and living things tend to adapt to their environment. Desert plants with a thick cuticle or submerged stomata to reduce water loss by changing the air are an example of adaptability. Organisms also show physical adaptations such as people exhibiting high altitude illnesses such as nausea, vomiting, heart palpitations, etc. and they become accustomed to the environment after some time.
Different types of biological responses include:
- Regulate
- conform
- Partial Controls
- Migration
- suspend (spores)
Population density changes mainly because of the following factors:
- Natality
- Mortality
- Immigration
- Emigration
One of the great abiotic features is Temperature.
Temperature is one of the strongest forces affecting living and nonliving things on Earth. Next, water is also a necessary abiotic factor in living organisms and the environment. Many organisms are altered due to the availability of less or more water. Finally, light. Light is the most important abiotic factor in plant survival and the last aspect of abiotic soils that greatly affects biodiversity and plant growth.
The Morphological Defense Mechanism is one of the most important protective mechanisms in plants such as the cactus whose leaves have been transformed into sharp thorns to prevent weeds from eating them. Some plants, such as using a morphological defense mechanism, have the edges of their spiny leaves or sharp edges that prevent insects from eating them.
