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. The role of abiotic factors, such as temperature and water, in survival and how most organisms survive between 0°C and 40°C is explained.

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

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.

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. 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. 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

• They regulate their internal conditions only to some limited extent.
• They can also 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 the features that improve their survival chances in its habitat of an organism to reproduce and multiply. 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

• 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 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: 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

N_t + 1 = N_t + [(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 occurs 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 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 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 another species is harmless or harmless.
• 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.

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