A biotic factor is a living thing that has an impact on another population of living things or on the environment. Abiotic factors do the same thing, but they are non-living. Together, biotic and abiotic factors make up an ecosystem. To survive, biotic factors need abiotic factors. In turn, biotic factors can limit the kinds and amounts of biotic factors in an ecosystem. 
Biotic factors are both organisms and the food the organisms eat. There are 3 categories of biotic factors, autotrophs, heterotrophs, and detritivores. The word autotroph means “self-feeder.” Also known as producers, the organisms in this category are mostly green plants and algae which make their own food through photosynthesis. The energy that they store serves as food for the consumers and decomposers (see below) either directly or indirectly. Autotrophs that don’t use photosynthesis to make their food use another process called chemosynthesis. In this case, organisms take organic material from their environment and transform it into organic nutrients, without the need for sunlight. A good example of this are the specialized bacteria that live near hydrothermal vents in the ocean and extract hydrogen sulfide from the water. Autotrophs use some of the energy they make to change elemental carbon into organic compounds (called carbon fixation) during photosynthesis or chemosynthesis. Although they feed on simple food sources, autotrophs are the base that drives the entire ecosystem. Heterotrophs (“other feeders”) are consumers in the ecosystem. They eat more complex organisms like plants and/or animals. Some examples of heterotrophs are bacteria, protists, fungi, herbivores (deer, cows, sheep), carnivores (bears, lions, dogs), and omnivores (birds, squirrels, rats, and humans). In fact, about 95% of all living things on Earth are heterotrophs. Unlike autotrophs, heterotrophs don’t have to fix carbon, so they can take advantage of all the energy from the food they eat. Detritivores are also consumers but they get their own category because of what they feed on. These organisms are also referred to as the decomposers, and they either eat dead organisms directly or break down dead things to get energy. Examples of detritivores are earthworms, fungi, dung beetles, millipedes, sea stars, and fiddler crabs. The complex cycle of interaction between biotic and abiotic factors continues as the decomposers clean up after the producers and consumers, but serve as food for the heterotrophs at the same time. The non-living abiotic factors control which organisms live in an ecosystem, where they live, and how many of them are there. Even slight changes in abiotic factors can have a significant effect on organisms in and ecosystem. Broadly, there are 3 categories of abiotic factors, climatic, edaphic, and social. Climatic factors are components such as water, sunlight, humidity, climate, temperature, and pH. For organisms that live in the water, sound waves, tides, water clarity, sunlight exposure, and pressure are also considered abiotic factors. Living organisms can take advantage of abiotic factors. For example, the wind can disperse seeds in the air which helps with pollination and gives plants the opportunity to spread. The wind is also a great example of an abiotic factor that affects many others. For example, wind direction and speed can affect humidity. Edaphic comes from the Greek word edaphos which means floor. It refers to abiotic factors like the geography of the land, and soil characteristics such as the mineral content. The topography of the land such as elevations, mountains, valleys, depressions, and slopes all contribute to the characteristics of an ecosystem. Similarly, soil characteristics like composition, texture, structure, and density determine what creatures can live there, and which plants can grow. Social abiotic factors describe how human activity can impact the land and resources in the area. Humans have an impact on many features of an ecosystem, but social factors are most likely to cause to larger-scale change. Thus, they can have profound impacts on other abiotic factors, biotic factors, entire ecosystems, and even entire biomes. Examples of social abiotic factors are clear-cutting of forests, mining, dam building, and farming. Bibliography
Population biology is a field of study that explores populations and how they interact with their environment. Scientists observe all factors influencing a population within an ecosystem when gathering data about specific populations of interest. Often these observations are vital to decisions made about how to protect a species. Environmental factorsEnvironmental factors that influence populations are divided into two categories – abiotic and biotic factors. Abiotic factors refer to the non-living physical and chemical elements found in an ecosystem such as rainfall, temperature, pH, sunlight, shelter and day length. Biotic factors refer to the living or once-living organisms in an ecosystem and their impacts such as predation, competition, food supply, human impacts and parasites. Environmental factors such as rainfall, climate, predators, shelter and food availability can change. Often, these factors play an important role in the survival of populations. Some factors change from day to day or season to season. Some, like food availability and predation, may vary over several years. A species that successfully survives in an environment has adapted to tolerate any minimal or seasonal fluctuations in these factors. For each factor, there is an optimum range where a species will thrive. If conditions change, organisms that can will move to live within the optimal conditions for survival. On either side of the optimum range, conditions can become difficult. This is referred to as a stress zone. Beyond the stress zone is the zone of intolerance. In this zone, individuals – and entire populations – may die. Most environments have one factor that determines the distribution of a species. This is known as Liebig’s law of the minimum. This critical factor is called the limiting factor. For aquatic species, it may be water temperature or tidal exposure. For birds like the takahē, it could be food availability.
Interspecific relationships are a biotic factor that describe the interactions between organisms within their environment. These interactions may have negative, positive or neutral effects on either species’ ability to survive and reproduce. The major types of species interactions are predation, competition, parasitism, mutualism, commensalism and amensalism. Populations dynamicsAll the organisms of the same species found in a particular region are called a population. The distribution of a population is determined by limiting factors. A population can vary in density (number of individuals in a population), distribution (the size of the population’s area and how the population is spread out in this area) and age structure. Populations change over time. Natality (birth rate) and mortality (death rate) are two aspects that control the age structure of a population. The relationship between the two aspects can be plotted on a survivorship curve. Individuals can also migrate to other groups or start new groups, and this can lead to changes in the genetic make-up of populations. Genetic drift can cause big losses of genetic variation for small populations. Reduced genetic variation can impact the ability for the population to be able to adapt to new selection pressures such as changes in available resources or other abiotic and biotic factors. Changes to allele frequencies in populations can have dramatic effects such as bottleneck and founder effects. For takahē, the rapid decline of the population meant that the gene pool is limited to the few individuals that survived and reestablished the population. Measuring population sizes can be done using a number of different methods such as direct counts or sampling using quadrats or transect lines. Population density is calculated as the mean number of individuals per quadrat divided by the area of the quadrat, and the population size can be calculated by multiplying the density by the area of distribution |
How do abiotic and biotic factors work together to influence population size
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