Organisms and Population

The chapter Organisms and Populations discusses key ecological concepts like how organisms interact with their environment and how populations grow and change. It explains the role of abiotic factors such as temperature and water in survival, and that most organisms thrive between 0°C and 40°C.

It also introduces population dynamics, covering features like population size, density, birth rate, and death rate. Models like logistic growth (dN/dt = rN[(K–N)/K]) help explain how populations stabilise over time. Real-life examples, such as Gause's competition experiments and mutualism between clownfish and sea anemones, help illustrate ecological relationships clearly. This chapter forms a base for advanced studies in Biology like ecology, conservation biology, and environmental management, making it important for Class 12 to NEET level.

This Story also Contains

1. Major Abiotic Factors Affecting Organisms and Populations
2. Responses to Abiotic Factors
3. Adaptations
4. Population Attributes
5. Population Regulation
6. Recommended Video on Organisms and Populations

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.

Also Read:

• Ecosystem
• Biotic and abiotic
• What Are The Types Of Interactions Between Organisms?

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 (dogs, cats, red algae) can tolerate wide ranges of temperatures, whereas stenothermal organisms (anaconda, crocodile, penguin) 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.
• The survival characteristics of an organism are affected by the characteristics of the water (pH and salt levels).
• Euryhaline species (such as crabs, and mollyfish) 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. The reactions help them survive and live under changing conditions. There are two major categories of response to abiotic factors:

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.

Partial Regulators

Regulate their internal conditions only to some limited extent but adapt when environmental conditions exceed their regulatory ability.

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 characteristics that enhance the survival chances or ability of an organism to reproduce within its habitat. 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

High-altitude people often experience symptoms of altitude sickness, such as nausea and fatigue.

To cope, the body raises its count of red blood cells, thus increasing oxygen binding and breathing rates.

Behavioural Adjustments

Some animals have developed certain habits based on particular environmental factors, such as migrating or hibernating.

Population Attributes

The population has its specific features that make it different from the individual organism or the whole species. 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: Described as the number of children born over a period of time.

(ii) Death: Described as the number of species that died over a period of time.

(iii) Immigration: It is defined as the number of people who come to a habitat from different places for a period of time.

(iv)Emigration: It is defined as the number of types of populations that exit their habitat for other places.

If the Population density is N at time t, then its density at time t+1 is represented as

Nt + 1 = Nt + [(B + I) - (D + E)]

When overcrowding is represented by N during t, the birth rate is represented by B + I, while the mortality rate is represented by D + E.

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 then it is called an interspecific interaction.

(i) Predation: Cooperation when a deer is killed by an invader. This is important in keeping predators afloat. In plants, herbivores act as predators. In some plants, a variety of habits are found that help them to protect themselves from predators. It may include thorns such as preservatives or protective substances such as caffeine, nicotine, quinine, etc., used for commercial purposes.

(ii) Competition: An interaction between an 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 the Gause Policy on Competitive Exclusion. The two adjacent models will compete for the same services and are not competitive so the lower one will be released during the competition.

(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 bird's nest while the host incubates them.

(iv) Commensalism: An interdependence of species where it is recognized 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 will benefit from each other. Examples are lichens (the relationship between algae and fungi), and mycorrhiza (the symbiotic relationship between fungi and high plant roots).

(vi) Amensalism: An interaction between an organism in which one species is harmed while another species is harmless or harmless.

Population Regulation

Population regulation prevents size and growth in the process of keeping the ecosystem stable.

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 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.

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