Dear Readers, Welcome to Ecology Interview Questions and Answers have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of Ecology Interview Questions. These Ecology Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many IT & Non IT Industries.
Ecology is the field of Biology that studies the relations between living beings and between living beings and the environment.
Species is the set of living beings able to cross among themselves generating fertile offspring.
This concept however does not apply to individuals of exclusive asexual reproduction and other definitions have been proposed. For example, "species is a set of living beings that evolve in a common manner all of them considered ancestors of the same type in relation to common descendants".
Population is the set of individuals of the same species found in a given place in a given time.
Community is the set of populations of living beings that live in the same region and interact with each other.
In Ecology population is a set whose members (living in a given place in a given time) are part of the same species. Community is a set of populations of different species (living in a given place in a given time).
Ecological niche is the set of peculiar activities, resources, and strategies that a species explores to survive and reproduce. Habitat is the place where the species lives to explore its ecological niche.
In other words, it can be said that habitat is the "address" of the species and the ecological niche is the "profession" of the species.
Biotic factors are the living beings (plants, animals, and microorganisms) that are part of a given environment.
Image Diversity: biotic factors
Abiotic factors are the nonliving elements that constitute a given environment, like light, temperature, minerals, water, gases, atmospheric pressure, etc.
Image Diversity: abiotic factors
Ecosystem is a system composed of biotic and abiotic factors in interaction.
Image Diversity: ecosystem
Biosphere is the set of all of the ecosystems of the planet.
Autotrophic beings are those that can produce their own food, i.e., that make organic material from inorganic compounds. Heterotrophic beings are those that need to incorporate organic material to nourish them. Therefore, heterotrophs depend on the production of the autotrophs.
Autotrophic beings make organic material by photosynthesis or by chemosynthesis. There are photosynthetic autotrophs, like plants, and chemosynthetic autotrophs, like some bacteria.
Biome is a prevailing ecosystem constituted by similar biotic and abiotic factors present in one or more regions of the planet.
The major terrestrial biomes are tundras, taigas (or boreal forest), temperate forests, tropical forests, grasslands and deserts.
Tundras have vegetation formed mainly by mosses and lichens. In the fauna the dense furred animals, like caribous, musk oxen and polar bears, and migratory birds are found.
Biomes - Image Diversity: tundras
Taiga, or the boreal forest, is characterized by coniferous trees, pine forests. There are also mosses, lichens, small bushes, and angiosperms. In the taiga many mammals, like moose, wolves, foxes and rodents, migratory birds and great diversity of insects are found.
Biomes - Image Diversity: taigas
In the temperate forest, deciduous trees predominate. Mammals are found in great number, like bears and deers.
Biomes - Image Diversity: temperate forests
Deciduous trees are plants that lose their leaves in a period of the year. In the case of the deciduous of the temperate forest, the fall of the leaves occurs in the autumn. The loss of leaves is a preparation to face the cold months of the winter: roots, stem and branches are more resistant to low temperature and snow than the leaves; without leaves the metabolic rate of the plant is reduced; the decaying fallen leaves help to nourish the soil.
Biomes - Image Diversity: deciduous trees
Tropical rain forests, like the Amazon forest and the Congo forest, are typically located in low latitude, i.e., in the equatorial and tropical zones.
Biomes - Image Diversity: tropical forests
In the vegetation of the tropical forests, broad-leafed evergreen trees predominate. On the top of the trees, epiphytes and lianas grow. Many varieties of pteridophytes can be found in these forests. Regarding the fauna, the abundance, and diversity is also great: there are monkeys, rodents, bats, insectivores, felines, reptiles, aves, amphibians, and invertebrates, mainly insects.
The biodiversity of these ecosystems can be explained by the great availability of the main abiotic factors for photosynthesis. Since these factors are abundant, plants can perform maximum photosynthetic activity, living and reproducing easily. With great amount and diversity of producers (autotrophs), the consumers (heterotrophic animals and microorganisms) also have abundant food and a complex food web emerges creating many different ecological niches to be explored. So it is possible the appearing of varied living beings as well as the existence of large populations.
In tropical forests, tall trees of several species have their crowns forming a superior layer under which diverse other trees and plants develop forming other inferior layers. From the upper layer to the inferior layers the penetration of light lowers gradually and the exposition to wind and rain, the moisture and the temperature vary. Different compositions of abiotic factor condition the prevailing of different vegetation in each layer.
Grasslands are mainly formed of herbaceous (nonwoody) vegetation: grass, bushes, and small trees.
Biomes - Image Diversity: grasslands
The steppe grasslands of North America are called prairies. The grasslands of South America are known as "pampas" (the steppe grassland) and "cerrado" (the savannah grassland).
Biomes - Image Diversity: prairies pampas cerrado
Grasslands may be classified into steppes and savannahs. In the steppes, the prevailing vegetation is grass, like in the pampas of South America and in the prairies of North America. The fauna is mainly formed by herbivores, like rodents and ungulates. The savannahs present small trees, like for example the Brazilian cerrado or the African savannahs. The fauna is diverse; in the Brazilian cerrado there are animals like emus, lizards, armadillos, jaguars, etc., and many types of insects; the African savannahs are the home of great herbivores and carnivores, like zebras, giraffes, antilopes, lions and leopards.
Biomes - Image Diversity: savannah
The predominant fauna of the desertic ecosystems is formed by reptiles, like lizards and snakes, terrestrial arthropods and small rodents. In these areas plants very adapted to dry climate may be found, like the cactus, that are plants that do not have real leaves and thus lose less water, along with grasses and bushes near places where water is available.
Biomes - Image Diversity: deserts
Amphibians are terrestrial vertebrates extremely rare in desertic environments (although there are few species adapted to this type of ecosystem). Amphibians are rare in deserts because they do not have permeable skin and so they easily lose water by evaporation and desiccate. They also need an aquatic environment to reproduce, since their fecundation is external and their larva is water-dependent.
Plankton, nekton, and benthos are the three groups into which aquatic living beings may be divided.
The plankton is formed by the algae and small animals that float near the water surface carried by the stream. The nekton is composed of animals that actively swim and dive in water, like fishes, turtles, whales, sharks, etc. The benthos comprehends the animals ecologically linked to the bottom, including many echinoderms, benthonic fishes, crustaceans, mollusks, poriferans and annelids.
Biomes - Image Diversity: plankton nekton benthos
Phytoplankton and zooplankton are divisions of the plankton. The phytoplankton comprehends the autotrophic floating beings: algae and cyanobacteria. The zooplankton is formed by the heterotrophic planktonic beings: protozoans, small crustaceans, cnidarians, larvae, etc.
A large number of photosynthetic beings is found in the plankton, i.e., in the surface of aquatic ecosystems. This is because light is abundant on the surface.
The primary energy source for life on earth is the sun. The sun plays the important role of keeping the planet warmed and it is the source of the luminous energy used in photosynthesis. This energy is converted into organic material by the photosynthetic autotrophic beings and consumed by the other living beings.
Image Diversity: the sun
The main means by which autotrophs obtain energy is photosynthesis. (There are also chemosynthetic autotrophs.)
Image Diversity: photosynthesis
Algae and cyanobacteria of the phytoplankton are the organisms that contribute most for the production of molecular oxygen.
Image Diversity: phytoplankton
In Ecology, autotrophic beings are called producers because they synthesize the organic material consumed by the other living beings of an ecosystem.
An ecosystem cannot exist without producers.
Heterotrophs are divided into consumers and decomposers. An ecosystem can exist without consumers but it cannot be sustained without decomposers. Without the decomposers, the organic material would accumulate causing environmental degradation and later death of the living beings.
Food chain is the linear not branched sequence in which a living being serves as food for the other, from the producers until the decomposers.
Image Diversity: food chain
The energy flux along a food chain is always unidirectional, from the producers to the decomposers.
Tropic levels correspond to positions on a food chain. Therefore, producers always belong to the first tropic level and decomposers to the last tropic level, consumers that eat directly the producers belong to the second tropic level and so on.
There is no limit regarding the number of tropic levels on a chain, since many orders of consumers can exist.
Primary consumers are living beings that eat autotrophic beings, i.e., they eat the producers. Primary consumers always belong to the second tropic level of a chain.
A food chain cannot have consumers of superior orders without having the consumer of the inferior orders. A consumer however can participate in several different chains not always belonging to the same consumer order in each of them.
The chain concept is a theoretical model to study the energy flux in ecosystems. Actually, in an ecosystem the organisms are part of several interconnected food chains, forming a food web. Therefore, the chain is a theoretical linear sequence and the web is a more realistic representation of nature in which the food chains interconnect forming a web.
Image Diversity: food web
The three types of tropic pyramids studied in Ecology are the numeric pyramid, the biomass pyramid, and the energy pyramid.
Generally, the variable dimension of the pyramid is the width and the height is always the same for each represented strata of living beings. The width therefore represents the number of individuals, or the total mass of these individuals or the available energy in each tropic level.
Image Diversity: tropic pyramids
Numeric pyramids represent the number of individuals in each tropic level of a food chain.
Image Diversity: numeric pyramids
In a numeric pyramid the base corresponds to the first tropic level, i.e., to the producers. The top level of the pyramid corresponds generally to the last consumer order of the food chain (since the number of individual decomposers, most of them microorganisms, is too large to be represented).
Image Diversity: decomposers
Since the numeric pyramid represents the quantity of individuals in each trophic level of the food chain, inferior tropic levels with fewer individuals than the superior tropic levels may exist. For example, a single tree can serve as food to millions of insects.
If an intermediate level of a numeric pyramid has its variable dimension decreased, i.e., if the number of individuals of such level is reduced, the number of individuals of the level below will increase and the number of individuals of the level above will be reduced. That happens because the individuals of the level below will face less predators and the individuals of the level above will have less available food.
Biomass pyramids represent the sum of the masses of the individuals that participate in each tropic level of a food chain.
Image Diversity: biomass pyramids
When biomasses are compared often, the concept of dry mass is used. The dry mass is the total mass less the water mass of an individual. The total mass is also called fresh mass. To use dry mass instead of fresh mass is utile because among living beings, there are differences related to the proportion of water within their body and such differences can distort the quantitative analysis of incorporated organic material.
Energy pyramids represent the amount of available energy in each tropic level of the food chain.
Image Diversity: energy pyramids
The luminous energy used in photosynthesis is transformed into chemical energy.
A superior tropic level always has less available energy than inferior tropic levels. This is because in each tropic level only a fraction of the organic material of the level below is incorporated into the consumers (into their bodies), the other part is eliminated as waste or is used in the metabolism as energy source. Therefore it is never possible to have energy pyramids with inverted conformation, i.e., with the tip to the bottom and the base to the top. It is also not possible to have superior tropic levels with variable dimension larger than inferior ones. In every energy pyramid, from the base to the top, the size of the variable dimension decreases.
Gross primary production of an ecosystem, or GPP, is the quantity of organic material found in a given area in a given period.
Since only autotrophs produce organic material and photosynthesis is the main production process, GPP is a result of the photosynthesis.
Mainly water and light, but also mineral salts, temperature, and carbon dioxide are factors that interfere with the gross primary productivity.
Part of the organic material synthesized by the producers is consumed as energy source for the metabolism of the own producer individual. Other part is incorporated (into the body) and become available to heterotrophic beings of the ecosystem. In each following tropic level part of the organic material is used in the metabolism of the individuals of the level, other part is eliminated as waste and only a fraction is incorporated and become available as food for the following level.
Net primary production is the gross primary productivity less the organic material consumed as energy source in the metabolism of the producers: NPP = GPP - (organic material spent in aerobic respiration). It represents the organic material available in the first tropic level. < /FONT >
The base of the energy pyramids must represent the NPP and not the GPP since the idea of these pyramids is to show the available energy in each trophic level of the food chain.
Biogeochemical cycles are representations of the circulation and recycling of matter in nature.
The main biogeochemical cycles studied in Ecology are the water cycle, the carbon cycle, and the nitrogen cycle.
Water is the main solvent of the living beings and it is necessary practically for all biochemical reactions, including as reagent of photosynthesis. Many properties of water are very important for life.
Carbon is the main chemical element of organic molecules; carbon dioxide is also reagent of photosynthesis and product of the energetic metabolism of the living beings.
Nitrogen is a fundamental chemical element of amino acids, the building blocks of proteins that in their turn are the main functional molecules of the living beings; nitrogen is also part of the nucleic acid molecules, the basis of reproduction, heredity, and protein synthesis.
The water cycle represents the circulation and recycling of water in nature.
Liquid water on the planet surface is heated by the sun and turns into water vapor that gains the atmosphere. In the atmosphere large volumes of water vapor, form clouds that when cooled precipitate liquid water as rain. Therefore, water comes back to the planet surface and the cycle is completed. As possible steps of the cycle, water may still be stored in subterranean reservatory or under the form of ice in mountains and oceans and it may also be used in the metabolism of living beings, incorporated into the body of the individuals or excreted through urine, feces, and transpiration.
Image Diversity: the water cycle
The sun can be considered the motor of the water cycle because upon its energy the transformation of liquid water into water vapor depends. Therefore, the sun is the energy source that makes water to circulate in nature.
The carbon cycle represents the circulation and recycling of the chemical element carbon in nature because of the action of living beings.
Photosynthetic beings absorb carbon as carbon dioxide available in the atmosphere and the carbon atoms become part of glucose molecules. During the cellular respiration of these beings, part of this organic material is consumed to generate ATP and in this process, carbon dioxide is returned to the atmosphere. Other part is incorporated by the photosynthetic organisms into the molecules that compose their structure. The carbon atoms incorporated into the producers are transferred to the next tropic level and again part is liberated by the cellular respiration of the consumers, part becomes constituent of the consumer body and part is excreted as uric acid or urea (excretes later recycled by decomposer bacteria). Therefore, carbon absorbed by the producers in photosynthesis returns to the atmosphere through cellular respiration along the food chain until the decomposers that also liberate carbon dioxide in their energetic metabolism. Under special conditions in a process, that takes millions of years carbon incorporated into organisms may also constitute fossil fuels stored in deposits under the surface of the planet as fossil fuels burn the carbon atoms return to the atmosphere as carbon dioxide or carbon monoxide. The burning of vegetable fuels, like wood, also returns carbon to the atmosphere.
The main biological process that consumes carbon dioxide is photosynthesis.
Carbon dioxide is made by producers and consumers through cellular respiration.
Fossil fuels, like oil, gas, and coal, form when organic material is preserved from the complete action of decomposers, generally buried deep and under pressure during millions of years. Under such conditions, the organic material transforms into hydrocarbon fuels.
Fossil fuels are natural reservatory of carbon. When oxygen is present, these fuels can be burned and carbon dioxide and carbon monoxide are released to the atmosphere.
The most abundant nitrogen-containing molecule found in nature is molecular nitrogen (N2). The air is 80% constituted of molecular nitrogen.
The nitrogen cycle represents the circulation and recycling of the chemical element nitrogen in nature.
The nitrogen cycle depends on the action of some specialized bacteria. Bacteria of the soil called nitrogen-fixing bacteria present in plant roots absorb molecular nitrogen from the air and liberate nitrogen under the form of ammonia. The decomposition of organic material also produces ammonia. In the soil and roots (mainly of leguminous), a first group of chemosynthetic bacteria called nitrifying bacteria, the nitrosomonas, produces energy consuming ammonia and releasing nitrite (NO2). The second group of nitrifying bacteria, the nitrobacteria, uses nitrite in chemosynthesis releasing nitrate (NO3). In the form of nitrate, nitrogen is then incorporated by the plants to be used as constituent of proteins and nucleic acids and the element then follows along the food chain. Nitrogen returns to the atmosphere by the action of denitrifying bacteria that use nitrogen-containing compounds from the soil and release nitrogen gas (molecular nitrogen).
Image Diversity: the nitrogen cycle
Leguminous crop rotation and other crop rotations are used in agriculture because in these plants many bacteria important for the nitrogen cycle live. The leguminous crop rotation (or conjointly with the main crop) helps the soil to become rich in nitrates that then are absorbed by the plants.
Green manure, the covering of the soil with grass and leguminous, is a way to improve the fixation of nitrogen and it is an option to avoid chemical fertilizers.
Biological diversity is the variety of species of living beings of an ecosystem. In ecosystems, more biodiverse, like tropical forests, a great variety of plants, microorganisms, and animals live; in ecosystems less biodiverse, like deserts, there are less variety of living beings.
Image Diversity: variety of life on Earth
The availability of abiotic factors, like light, moisture, mineral salts, heat and carbon dioxide, conditions more or less biodiversity of an ecosystem. Photosynthesis depends on water and light, and plants need mineral salts, carbon dioxide, and adequate temperature for their cells to work. In environments where these factors are not restrictive, the synthesis of organic material (by photosynthesis) is maximum, plants and algae can reproduce easier, the population of these beings increases, potential ecological niches multiply and new species emerge. The large mass of producers makes viable the appearing of a diversity of consumers of several orders. In environments with restrictive abiotic factors, like deserts, the producers exist in little number and less diversity, a feature that thus extends to consumers and conditions fewer ecological niches to be explored.
The vegetal stratification of an ecosystem, like the strata of the Amazon Rainforest, creates vertical layers with peculiar abiotic and biotic factors, dividing the ecosystem into several different environments. Therefore, in the superior layer near the crowns of big trees, the exposition to light, rain, and wind is greater but moisture is lower comparing to the inferior layers. As one goes down the strata, the penetration of light diminishes and moisture increases. Regarding the biotic factors, communities of each stratum present composition, features, food habits, and reproduction strategies, etc., also different. Such variations in the abiotic and biotic factors make the selective pressure upon the living beings also diversified, there are more ecological niches to be explored and more varied beings emerge during the evolutionary process.
The natural soil of the Amazon Rainforest is not too fertile but it is enriched by the vegetal covering made of leaves and branches that fall from the trees. Deforestation reduces this enrichment. In deforestation zones, the rain falls directly on the ground causing erosion, "washing" large areas (leaching) and contributing to make the soil even less fertile. Besides that, the deforestation disallows the recycling of essential nutrients for plants, like nitrogen. In this manner, those regions and their neighboring regions undergo desertification.
Image Diversity: Amazon Rainforest
In ecosystems with more biodiversity, the food webs and ecological interactions among living beings are more complex and diverse. In these ecosystems, environmental changes can easier be compensated by the multiplicity of available resources, foods, and survival options.
In ecosystems with less biodiversity, the individuals are more dependent on some beings that serve them as food and they interact with a small number of different species. In these ecosystems, generally, abiotic factors are restrictive and the species are more specialized to such conditions and more sensitive to environmental changes. Even small environmental harms can cause big disturbances in the equilibrium of the ecosystem.
Monoculture means that in a large area a single crop (only one species of plant) is cultivated. Therefore, monoculture does not contribute to the formation of a community with great variety of species in the area. Since there is only a single type of producer the types of consumers that can live in the area are also restricted.
Very biodiverse areas present enormous economic potential. They can be source of raw material for the research and production of medicines, cosmetics, chemical products, and food. They are depository of genetic wealth that can be explored by biotechnology. They are source of species for agriculture. They can also be explored by the ecological tourism.
The biggest dangers to the biological diversity today are fruits of the human action. The main of them is the destruction of habitats caused by the growth of the cities, deforestation, pollution, and fires. The second is the invasion of ecosystems by nonnative species introduced by humans; these species change the equilibrium of ecosystems causing harm. Other big dangers are the predatory hunting and fishing and the global warming.
Inharmonious, or negative, ecological interaction is that in which at least one of the participating beings is harmed.
Ecological interactions are classified as intraspecific or interspecific interactions and as harmonious or inharmonious interactions.
Intraspecific ecological interactions are those between individuals of the same species. Interspecific ecological interactions are ecological interactions between individuals of different species.
Inharmonious, or negative, ecological interaction is that in which at least one of the participating beings is harmed.
Harmonious, or positive, ecological interaction is that in which none of the participating beings is harmed.
The main harmonious intraspecific ecological interactions are colonies and societies. The main inharmonious intraspecific ecological interactions are intraspecific competition and cannibalism.
Symbiosis and Other Interactions - Image Diversity: colonies animal societies
Colonies are functional integrated aggregates formed by individuals of the same species. Colonies are often confounded with a single individual. Examples are the coral reefs, by-the-wind sailors, and filamentous algae.
Societies are interactions for labor division and collaboration among individuals of the same species. Human societies are examples of ecological societies; other species, like bees, ants, termites, wolves and dolphins form societies.
Competition is the ecological interaction in which the individuals explore the same ecological niche or their ecological niches partially coincide and therefore competition for the same environmental resources takes place.
Competition is harmful for all participating beings and thus it is classified as an inharmonious (negative) ecological interaction.
Symbiosis and Other Interactions - Image Diversity:
Intraspecific competition practically occurs in all species, for example, the competition of humans for a job.
In cannibalism an individual eat other of the same species (occurs in some insects and arachnids). Since it is an interaction between beings of the same species and at least one of them is harmed (the other is benefited) the classification as inharmonious intraspecific ecological interaction is justified.
Symbiosis and Other Interactions - Image Diversity: cannibalism
The main harmonious interspecific ecological interactions are protocooperation, mutualism and commensalism. The main inharmonious interspecific ecological interactions are interspecific competition, parasitism, predatism and ammensalism.
Protocooperation is the ecological interaction in which both participants benefit and that is not obligatory for their survival. Protocooperation is a harmonious (positive) interspecific ecological interaction. Examples of protocooperation are: the action of the spur-winged plover that using its beak eats residuals from crocodile teeth; the removal of ectoparasites from the back of bovines by some birds that eat the parasites; the hermit crab that live inside shells over which sea anemones live (these offer protection to the crab and gain mobility to obtain food).
Symbiosis and Other Interactions - Image Diversity: protocooperation
Mutualism is the ecological interaction in which both participants benefit and that is obligatory for their survival. Mutualism is a harmonious (positive) ecological interaction. Mutualism is also known as symbiosis. Examples of mutualism are: the association between microorganisms that digest cellulose and the ruminants or insects within which they live; the lichens, formed by algae or cyanobacteria that make organic material for the fungi and absorb water with their help; nitrifying bacteria of the genus Rhizobium that associated to leguminous offer nitrogen to these plants.
Symbiosis and Other Interactions - Image Diversity: mutualism
Commensalism is the ecological interaction in which one individual benefit while the other is not benefited neither harmed. Commensalism is a harmonious (positive) ecological interaction, since none of the participants is harmed. Example of commensalism are the numerous bacteria that live in the skin and in the digestive tube of humans without being pathogenic neither beneficial. They are innocuous bacteria living in commensalism with humans.
Symbiosis and Other Interactions - Image Diversity: commensalism
Commensalism may involve obtention of food (for example, the innocuous bacteria of the human guts), shelter or support (epiphytes on trees) and transportation (pollen carried by insects or birds). The commensalism that involves obtention of shelter is also called inquilinism.
Examples of interspecific competition are the dispute among vultures, worms, flies, and microorganisms for carrions and the competition between snakes and eagles for rodents.
Symbiosis and Other Interactions - Image Diversity: interspecific competition
Parasitism is the ecological interaction in which a being lives at the expense of other. The parasite often does not cause immediate death of the host since it needs the host alive to survive.
Parasitism is an inharmonious (negative) interspecific ecological interaction, since although one participant benefit the other is harmed.
Symbiosis and Other Interactions - Image Diversity: parasitism
Classical examples are the parasites of humans (host), like the trypanosome that causes Chagas' disease, the HIV virus (AIDS), the bacteria that causes tuberculosis, the schistosome that causes schistosomiasis, the hookworms, etc. Other examples are tree (host) and parasitic helminths (parasite), dog (host) and lice (parasite), cattle (host) and tick (parasite), etc.
Predatism is the ecological interaction in which one individual mutilates or kills other to get food. Predatism is an inharmonious (negative) ecological interaction since one participant is harmed.
Symbiosis and Other Interactions - Image Diversity: predatism
Herbivorism is the form of predatism in which first order consumers feed from producers (plants or algae). For example, birds and fruits, humans and eatable vegetable, etc. (There are proposals to consider the herbivorism of leaves a form of parasitism and the herbivorism of entire plants and seeds a form of predatism).
Ammensalism is the ecological interaction in which an individual harms other without obtaining benefit. Ammensalism is an inharmonious (negative) ecological interaction since one participant is harmed.
(Sometimes it is wrongly said that ammensalism is a form of ecological interaction in which an organism releases in the environment substances that harm another species; this situation is indeed an example of ammensalims but the concept is not restricted to it.)
One of the best examples of ammensalism is the one established between humans and other species under extinction due to human actions like habitat devastation by fires, ecological accidents, leisure hunting, etc. Other example is the red tide, proliferation of algae that by intoxication can lead to death of fishes and other animals.
Ecological succession is the changing sequence of communities that live in a ecosystem during a given time period.
Image Diversity: ecological succession
Pioneer species are those first species that colonize places where previously there were no living beings, like, for example, algae that colonize bare rocks. In general, pioneers species are autotrophs or maintain harmonious ecological interaction with autotrophic beings (like autotrophic bacteria, herbaceous plants, lichens).
The pioneer community is formed of species able to survive under hostile environments. The presence of these species modifies the microenvironment generating changes in abiotic and biotic factors of the ecosystem undergoing formation. Therefore, they open way to other species to establish in the place by the creation of new potential ecological niches.
Primary ecological succession is the changing sequence of communities from the first biological occupation of a place where previously there were no living beings. For example, the colonization and the following succession of communities are in a bare rock.
Secondary ecological succession is the changing sequence of communities from the substitution of a community by a new one in a given place. For example, the ecological succession from the invasion of plants and animals are in an abandoned crop or land.
The climax stage is the stage of the ecological succession in which the community of an ecosystem becomes stable and does not undergo significant changes. In the climax community practically all ecological niches are explored and the biodiversity is the greater possible. In this stage the biomass, the photosynthesis rate and the cellular respiration reach their maximum levels and thus the net primary production (NPP = organic material made by the producers - organic material consumed in the cellular respiration of the producers) tends to zero. At the climax, the amount of oxygen released by photosynthesis is practically equal to the oxygen consumed by respiration. (This is one more reason why it is wrong to say that the Amazon Rainforest, an ecosystem at climax stage, is "the lung" of the earth. Other reasons are lungs are not producers of oxygen; the algae and cyanobacteria of the phytoplankton are the main producers of the molecular oxygen of the planet.)
Biodiversity, the number of living beings, and the biomass of an ecosystem tend to increase as the succession progresses and they stabilize when the climax stage is reached.
At the initial stage of the succession the use of carbon dioxide and the fixation of carbon into the biomass are high, since the total number of living beings in the ecosystem is increasing. At the climax stage, the use of carbon dioxide by photosynthesis equals the production by cellular respiration and the fixation of carbon into the biomass tends to zero.
In Biology population is a set of individuals of the same species living in a given place and in a given time.
Population Ecology - Image Diversity: world human population
Population density is the relation between the number of individuals of a population and the area or volume they occupy. For example, in 2001 the human population density of the United States (according to the World Bank) was 29,71 inhabitants per square kilometer and China had a population density of 135,41 humans per square kilometer.
Population growth rate (PGR) is the percent variation between the numbers of individuals in a population in two different times. Therefore, the population growth rate can be positive or negative.
Migration is the moving of individuals of a species from one place to other. Emigration is the migration seen as exit of individuals from one region (to other where they will settle permanently or temporarily). Immigration is the migration seen as the settling in one region (permanently or temporarily) of individuals coming from other region. Therefore, individuals emigrate "from" and immigrate "to".
The main factors that make populations grow are births and immigration. The main factors that make populations decrease are deaths and emigration.
Examples of migratory animals are: southern right whales from Antarctica, that procreate in the Brazilian coast; migratory salmons that are born in the river, go to the sea and return to the river to reproduce and die; migratory birds from cold regions that spend the winter in tropical regions; etc.