The Principles of Ecology [BIOLOGY]

• Abiotic factors: Air, Soil, Salinity, Temp, Light, Water, Minerals, pH, Humidity

  Biotic factors: Animals, Plants, Bacteria, Archaea, Fungi, Protists
• The tropics which lie between the Tropic of Cancer in the north and the Tropic Capricorn in the south experience the greatest amount of sunlight and the least seasonal variation (hence why we in the Philippines only have dry and wet seasons).
• Those that experience the four seasons lie in temperate zones and these areas lie between the Arctic Circle and the Tropic of Cancer in the north; and the Antarctic Circle and the Tropic of Capricorn in the south. The polar zones are covered in ice due primarily to their location.
• This movement of air created what is known as the atmospheric circulation cells and for those interested, they are the:

  • Hadley cells located in the tropics
  • Ferrel cells on temperate regions
  • Polar cells on either the north and south hemispheres
• The air movements in conjunction with the Earth’s rotation result in major global air patterns known as the prevailing winds. Because the Earth is spherical, its surface moves faster in the equator where it has the greatest diameter compared with other latitudes.
• In the tropics, the prevailing winds are known as the Easterlies or the Trade Winds (think of Amihan and Habagat in our country) while those in temperate regions are known as the Westerlies.
• The combination of the prevailing winds, Earth’s rotation, unequal heat absorption, and the locations and shapes of the continents create the ocean currents, the river-like flow patterns at the ocean’s surface. Ocean currents have profound effects on regional climates and can even explain the El Niño and La Niña phenomena and the distribution of aquatic organisms, like how upwelling areas in some peninsulas explain why Zamboanga have more sardines caught relative to other areas in the country.
• Biomes are major ecological associations that occupy a broad geographic region of land or water. Terrestrial biomes are primarily influenced by temperature and precipitation while aquatic biomes are defined by different abiotic factors with the main distinction being salinity
• Aquatic Biomes

  • Marine Biomes
  • Ocean
  • Intertidal Zone
  • Freshwater Biomes

  Terrestrial Biomes

  • Tropical forests
  • Savanas
  • Deserts
  • Chaparrals
  • Temperate grasslands
  • Temperate broadleaf forests
  • Coniferous forests (Taiga)
  • Tundra
  • Polar ice
• Ocean

  The pelagic zone of the oceans includes all open water while the seafloor is known as the benthic zone. Light diminishes with the ocean’s depth and the part where light is still visible is referred to as the photic zone. The latter usually measures a maximum of 200 m and can include both pelagic and benthic zones in shallow areas, which are parts of continents called the continental shelves.
• Ocean

  Organisms that drift with the currents are called plankton, those that swim or move independently are called nekton, while those limited to moving along the seafloor are referred to as the benthos
• Ocean

  In the photic zones, phytoplankton acts as autotrophs and provides energy for a diverse community of organisms. Zooplankton and many other animals are abundant in the pelagic photic zone. Coral reefs are located in the photic zones, because of their zooxanthellae, and provide habitats to various marine organisms.
• Interidal zone

  The intertidal zone is the area where the ocean meets land, and where the shore is pounded by waves during high tide but left exposed to the sun and drying winds on low tide. You can have rocky intertidal zones, which house many sedentary organisms such as barnacles and mussels, or sandy beaches, where clams and other predatory crustaceans bury themselves.
• Interidal zone

  An estuary occurs where freshwater merges with saltwater and so there are gradients to the saltiness, depending on whether you are towards the freshwater or saltwater end of the biome. Wetlands are biomes that mark the transition between an aquatic ecosystem and a terrestrial one. They can be covered by water permanently or periodically so they can support the growth of aquatic plants. Mudflats and marshes are coastal wetlands that often border estuaries and experience tidal fluctuations.
• Freshwater biomes

  Freshwater biomes fall into two broad categories: standing water and flowing water biomes. The former includes lakes and ponds while the latter involves streams and rivers. There are also freshwater wetlands that range from marshes to swamps and bogs.
• Tropical forests

  Tropical forests are found in equatorial areas where the temperature is warm and days are 11-12 hours long all year round. The forest structure is made of distinct layers that provide different habitats: emergent trees growing above a closed upper canopy, one or two layers of lower trees, a shrub understory, and a sparse ground layer of herbaceous plants
• Savannas are biomes dominated by grasses and scattered trees, and where the temperature is also warm all year round. There is also a relatively brief rainy season with the poor soil and lack of moisture preventing more trees from rooting (pun intended) and establishing themselves in the area. Grazing by animals and fires also limits invasion by trees.
• Deserts are the driest of all terrestrial biomes having low and unpredictable rainfall. Not all desert air is dry; some coastal portions of the Atacama and Namib desert in Africa are often shrouded in fog, but the ground remains extremely dry.
• Chaparrals are characterized by dense, spiny shrubs with evergreen leaves. The climate that supports such biomes is mainly due to cool ocean currents that circulate offshore, producing mild, rainy winters and hot, dry summers. And because of this, chaparrals are limited to small coastal areas such as California.
• Temperate grasslands have some features of savannas, but most are treeless, except where there are rivers or streams. The biome is found in regions with relatively colder winter temperatures. Fires and grazing also limit the growth of woody plants but do not harm the belowground grass shoots.
• Temperate broadleaf forests grow in regions with sufficient moisture to support large trees. In the Northern Hemisphere, deciduous trees are common in these forests. The mix of tree species varies widely, influenced by different factors such as regional climate, topography, and local soil conditions.
• Coniferous forests are dominated by cone-bearing evergreen trees. These include the northern coniferous forests, the taiga, that stretch along the latitude across North America and Asia below the Arctic Circle. The taiga is also found at cool, high elevations in more temperate latitudes on mountains..
• Tundra covers an expanse of areas of the Arctic between the taiga and the polar ice. The climate is often extremely cold, with little light for much of the autumn and winter. The arctic tundra is characterized by a continuously frozen subsoil, the permafrost, where only its upper parts thaw in summer.
• Polar ice covers land north of the tundra and the entire continent of Antarctica. The temperature in these regions is extremely cold and precipitation is very low. Only a small portion of these landmasses is free of ice or snow even during summer. Nevertheless, lichens and small plants such as mosses manage to survive. Invertebrates such as nematodes, mites, and wingless insects called springtails inhabit the frigid soil.
• Population ecology is concerned with changes in population size and the factors that regulate it over time. One important aspect of the population’s dynamics is population growth.
• Two important factors are important in shaping a population: density and dispersal. Population density refers to the number of individuals of a species per unit area. Because it is impractical or impossible to count all individuals in a population in most cases, ecologists use various sampling techniques to estimate the population densities. Dispersal or the dispersion pattern of a population refers to the way individuals are spaced within an area.
• A clumped dispersion pattern occurs when individuals are grouped in patches. It is the most common pattern in nature. This pattern is mainly because the resources required are unevenly distributed in a given area. For instance, you may see plants grow in a certain space on an open lot where you may presume the soil is ideal for their growth. Clumping in animals, meanwhile, is often due to uneven food distribution
• A uniform dispersion pattern often comes from interactions between individuals of the population. Some plants, through allelopathy, inhibit the growth of nearby plants that could compete for the same resources. Animals may become evenly dispersed due to territorial behavior.
• In random dispersion, individuals are spaced in an unpredictable manner and so there is no pattern. Plants may become randomly dispersed when their seeds go with the wind. However, varying habitat conditions and social interactions make random dispersion rare.
• Members of a community engage in interspecific interactions where they interact with individuals from a different species. Interspecific competition occurs when populations of two or more different species compete for the same, limited resources.
• In mutualism, both populations benefit. For example, the relationship between plants and their pollinators is mutual. Predation, herbivory, and parasitism are just a few types of interaction that lead to one species exploiting the other.
• Interactions

  • Competition
  • Mutualism
  • Predation
  • Herbivory
  • Parasitism
• Each species in a community has an ecological niche. This is the sum of its use of biotic and abiotic resources in the environment. That is to say, they fill and play a role in the environment they live in and everything it needs to continue existing. The previously mentioned types of interactions shape the niche of an organism and influence the communities’ trophic structure.
• The sequence of food transfer up each trophic level is known as a food chain. Starting at the bottom, the trophic level supports all others and consists of the autotrophs which ecologists call producers.
• All organisms in trophic levels above the producers are heterotrophs and their consumption depends on the output of producers. Herbivores are primary consumers. The trophic levels above them are made up of carnivores and insectivores and the trophic level could extend as long as one is consumed by another (secondary up to quaternary consumers are also observed in some food chains). Food chains are interconnected in nature, forming a food web.
• There is another trophic level where the consumers derive their energy from detritus and they consume it at different stages of decay. Scavengers feast on carcasses left behind by predators; detritivores feed on decaying organic material; while decomposers digest the organic molecules into their inorganic forms. The breakdown of organic material into inorganic ones is decomposition and it allows decomposers to recycle the nutrients, linking all trophic levels in the process.
• A community has species diversity which is defined by two components: species richness and relative abundance. Species richness is the number of different species in a community while relative abundance is the proportion of each species in the community. The species diversity of plants often affects the species diversity of animals in the community.
• Species diversity also has consequences for pathogens since most can only infect certain hosts or target species. Low species diversity is visible in many modern agricultural ecosystems since most crops are planted in monoculture, that is a single species is grown over a wide area. This is why agricultural fields can get devastated potentially when their plants get infected by pathogens.
• Severe disturbances, however, could alter communities drastically which may lead to different species colonizing the disturbed area and would again alter the community structure. The gradual replacement by a series of other species is the process known as ecological succession

  • Primary
  • Secondary
• Ecological succession begins in a virtually lifeless area, without soil, and is called primary succession. Examples would be areas left by a recent volcanic lava flow. Often, autotrophic bacteria are initially present. Lichens and moss which are blown as spores are the larger photosynthetic organisms that would grow there next.