Environmental factors and the adaptation of organisms

Ecology studies the interactions between organisms and their living and non-living environment, as well as the factors that influence the abundance and distribution of organisms.

Different species have different requirements for their environment. The environmental factors that organisms use, such as food, water and light, are called resources. An individual's resources can be divided into biotic and abiotic factors.

Biotic or living factors are related to other organisms in the community living in the same area. Biotic factors are individuals of the same species or another species that influence the success of a species. They can be food, predators, breeding partners, competing species, parasites or pathogens.

Abiotic or non-living factors have to do with the properties of land, air and water. Abiotic factors can be divided into chemical and physical factors. Chemical environmental factors include rock types, soil pH, salinity and nutrients. Physical environmental factors include the amount and quality of light, variations in temperature and precipitation, as well as wind.

The abiotic environmental factors that are important for organisms include water, nutrients, light, oxygen, heat, acidity and salinity. The more favourable the abiotic environment, the more species are present in the area, and the better the organisms grow and reproduce. No organism can survive without water, which is found in all living cells. The life functions of an organism are mainly based on chemical reactions that take place in water. Water is also one of the raw materials for photosynthesis, which powers almost all life on Earth.

One of the most important abiotic factors is sunlight. Plants need it for photosynthesis, together with water and carbon dioxide. In photosynthesis, plants produce sugar (glucose), which they use to grow and reproduce. The sugar and its derivatives are used by other organisms for food and energy, either directly (herbivores) or indirectly (predators). The amount and quality of light can vary between different regions and times of the year. In Finland, for example, the amount of sunlight is lower than at the equator for most of the year, while in summer it is available almost 24 hours a day. The sun's thermal radiation, or infrared radiation, is also an important environmental factor for life on Earth.

Other important abiotic factors for plants include nutrients (e.g. nitrogen, phosphorus and potassium), carbon dioxide needed for photosynthesis and the acidity (pH) of the soil. The solubility of nutrients in the soil depends on its acidity. Plant growth is severely limited when there is not enough nitrogen available. In water ecosystems, phosphorus often limits the growth of algae, while excess phosphorus can lead to the eutrophication of the ecosystem.

The minimum factor is the abiotic environmental factor that most limits the growth, occurrence and distribution of an organism. Depending on the species, the minimum factor can be any environmental factor, such as light, moisture or a nutrient. Nitrogen is often rare in soil in a form that plants can use, so it and phosphorus are minimum factors for many plant species. There can also be too much of a particular abiotic factor, such as water, in the environment. For example, plants adapted to desert environments do not thrive in rainforests.

The intensity of light, the duration of daylight and the amount of heat vary with latitude and season. In the equatorial tropics, conditions of temperature, light and precipitation are stable throughout the year. In polar regions, organisms have had to adapt to cold, darkness and seasonal food scarcity. Different species have adapted to different conditions through the process of evolution, and living organisms are thus distributed into almost every region of the planet.

Storms, tsunamis and forest fires can have a major impact on wildlife. The seedlings of trees are most affected by fire, while large trees are usually protected by their bark. On the other hand, forest fires are a natural part of forest regeneration, as the seeds of some plant species only germinate after a fire.

Through natural selection, species have adapted to different habitats, allowing populations to survive in new and changing environmental conditions. Species have evolved adaptations that can be passed on to their offspring and may thus become widespread in a population. For example, aquatic plants have adapted to life in water ecosystems and are therefore structurally different from terrestrial plants. Mutations that occurred in the ancestors of aquatic plants have contributed to their adaptation to water ecosystems. These mutations have been beneficial and have increased the fitness of the species. Gradually, they have become more widespread in the populations of the species.

Biogeography is a branch of biology and geography that deals with the geographical distribution of plants and animals. The distribution of a species depends on its environmental requirements, the availability of environmental factors, its adaptability and its ability to spread to new areas. The range of a species covers only those areas where conditions are suitable for the species to thrive, i.e. the regions in the species’ tolerance range.

The distribution of an organism is often limited by abiotic factors, such as heat conditions. For example, in Finland, the tick is mainly found in coastal regions and in the Finnish Archipelago. However, the species has gradually spread further northwards and into inland areas. Today, the tick's distribution covers the whole of southern and central Finland, and individuals have been found everywhere but the northernmost part of Lapland. Due to environmental conditions, regional differences in the prevalence of ticks are large. The most important environmental factors in terms of the tick’s distribution are humidity and temperature. When the temperature rises above 5 °C in spring, the ticks begin to move.

A species is not always able to spread to all areas where its habitat requirements are met. This may be due to geographical and biological dispersal barriers. Examples of geographical barriers include oceans, deserts and land masses. On the other hand, strips of land can act as dispersal corridors for terrestrial animals. A competing species or an efficient predator can also prevent the spread of a species.

The ranges of species vary in terms of the extent and uniformity of their distribution. The range of a species may consist of discrete areas (mosaic-like dispersal).

Cosmopolitan species (e.g. the brown rat) have spread to almost all continents, while endemic (native) species are restricted to a small geographical area. For example, many organisms found on isolated oceanic islands are endemic. An endemic species occurs only within its native range, which is often restricted. Some species now have a much narrower range than in the past. One such relic or remnant species is the crustacean species Saduria entomon found in the Baltic Sea.

Expanding the range of dispersal often benefits the species by avoiding the disadvantages caused by both interbreeding and overcrowding, such as competition, resource scarcity and disease.

The survival, growth and reproduction of each species depends on a wide range of abiotic and biotic environmental factors. These factors can be favourable to the species or beyond its tolerance range. Environmental conditions influence the function of the ecosystem, for example through the oxygen and sugar production of green plants. The availability of water and the environment’s temperature affect the photosynthetic efficiency of plants, and therefore influence their growth and reproduction. In turn, increased competition can reduce the favourable habitat and distribution of a species. Prolonged drought can reduce the sizes of populations and exceeding the temperature limit can cause mortality. This has been observed in Australian bats during forest fires, for example.

Species have adapted to specific local living conditions over a long period of time. As a result of climate change (increased temperatures, droughts, floods, extreme weather events), the conditions of many environments have changed too rapidly for living organisms, and many habitats are in the process of shrinking or disappearing completely. Global warming is already reflected in changes in the distribution of many species. The shift of the planet’s climatic zones towards the poles is shifting the location and extent of habitats favourable to various species. The distribution ranges of organisms can and have already shifted towards the poles. For example, some butterfly species have taken advantage of global warming by spreading northwards. On the other hand, organisms native to the Arctic tundra are at risk as the northern coniferous forest zone moves further north, while the Arctic Ocean is simultaneously limiting the northward movement of these organisms. For example, the polar bear has declined as the northern ice situation has become less favourable and habitats have shrunk, with the Arctic Ocean also acting as a dispersal barrier. As a result, Arctic species are unable to find suitable areas to disperse.

The impacts of climate change on the distribution and diversity of species varies across the globe. Changes in mean temperature and precipitation as well as the annual distribution of these factors are key drivers of weather patterns. They will cause major changes in the living conditions of ecosystems, testing the adaptive capacities of many species. These impacts are reflected in changes in the distribution and diversity of organisms.

However, the impacts of climate change are specific to ecosystems and species. Species can either adapt to the change or move to a more favourable area to survive. In the worst case scenario, a species may become extinct. This process is influenced by species-specific adaptive and dispersal capacities, species-specific environmental requirements within the ecological niche and the availability of suitable habitats. In any case, changes in the abundance of species and individuals disrupt the functioning of the ecosystem as a whole through complex ecological interactions (predation, parasitism, competition). 

Changes in ecological interactions also affect biodiversity. If you look at a pair of interdependent species, a decline in the population size of one species can cause a decline in the population of another species that is dependent on the first one. Species moving into new ranges may compete with native species and cause various diseases and disturbances to native flora and fauna. These disturbances include parasites, fungal diseases and bloodsucking insects.

On northern latitudes, organisms have had to adapt to seasonal variations in light and heat. In these regions, both plants and animals have to prepare for the cold winter. This can be seen when looking at nature in the autumn. For example, the leaves of plants change colour and begin to drop as photosynthesis stops, and migratory birds flock together and begin to move further south for the winter.

Over the course of evolution, overwintering species have had to adapt to environmental conditions through many structural and functional changes. Perennial plants "hibernate" through the winter, and many animals spend the winter in hibernation, brumation or winter sleep.

Many overwintering animals undergo changes in their behaviour and bodies related to snow, cold and winter foraging. One such peculiarity is that the skull of a shrew shrinks in winter and grows back again in spring. This reduces the mammal's need for food and energy in winter.

Forest birds, such as willow ptarmigans, spend all their time buried in the snow, except for when they search for food. Snow provides protection from the cold and predators. Small birds spend the whole of the short light period of the winter day searching for food, and some may also forage at dusk. By changing their behaviour, birds such as goldcrests can take advantage of the heat produced by each other. Birds spend the night side by side on tree branches, with the most peripheral individuals swapping places with those in the middle from time to time.

Some animals reduce their activity levels by spending the winter in winter sleep, hibernation or brumation because food and heat are scarce in winter. Common to all these wintering patterns is a slowing down of vital functions. Energy is saved by lowering the body temperature, heart rate and breathing.

Many poikilothermic animals, such as reptiles, amphibians and insects, spend the winter in brumation. Insects often overwinter as larvae or pupae instead of adults. Homeothermic animals can overwinter either in winter sleep or hibernation. For example, bears and badgers spend the winter in a deep winter sleep, while hedgehogs and bats slow down their vital functions more drastically in hibernation.

Plants and winter

Perennial plants, such as trees, store energy and nutrients for the winter in the overwintering parts of the plant (trunk, stem and roots) and use them for growth the following spring. In evergreen conifers, the water content of the cells decreases and the sugar content increases. The more concentrated the cell fluid, the lower its freezing point. This means that the cells do not freeze and break as easily, and their cold tolerance is improved. Many plants, such as conifers and mosses, are evergreen. They are able to begin photosynthesis and reproduction early in the spring because they have their leaves ready. For example, the hairy wood-rush overwinters as a deciduous rose, and therefore begins flowering early when other plants are just beginning opening their buds. Conifers can suffer from a lack of water in spring when the ground is still frozen and when the leaves begin to evaporate water as the temperature rises.

Even closely related species may have different wintering habits. The blueberry in the photo drops its leaves in autumn and overwinters leafless, while the lingonberry overwinters without shedding its leaves.