I describe Ecology as the study of various living organisms, their respective relationship with other organisms along with their responsiveness to the surrounding environment. Ecologists usually adopt the method of studying and analyzing Niches in order to better understand an organism and its survival. Niche is defined as “The role played by an organism in an ecosystem; its food preferences, requirements for shelter, special behaviours and the timing of its activities (eg; nocturnal, diurnal), interaction with other organisms and its habitat.” www.pde.state.pa.us/a_and_t/lib/a_and_t/Science_Glossary.doc
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A niche is usually classified as Realized niche, which is defined as the niche where living organisms’ persist, utilizing resources despite the presence of competition, co existence and predation, whereas a Fundamental niche is defined as an ideal niche containing abiotic conditions and resources providing suitable conditions for an organism to survive. This distinction was first proposed by Hutchingson (1957).
A realized niche is the potential space which an organism actually utilizes for its survival and growth. A species living in its realized niche may or may not utilize its niche to the fullest because of intra specific and also inter specific competition. Predators may also be a prime threat for a species in its realized niche. For example, if a sparrow is nesting on a particular tree in a forest, the nesting tree including a limited area around it is considered as a realized niche for that sparrow whereas the chunk of forest in which the nesting tree is located is considered as the fundamental niche for that sparrow.
The prime confusion which arouse over the existence of the cleaner fish and their impact on the other fish discussed in the paper “Cleaner Fish Drives Local Fish Diversity on Coral Reefs” by Alexandra S. Grutter et.al. (2003) can be clarified to some extent based on the realized and fundamental niche concept. The experimental design adopted by the authors showed that the existence of the cleaner fish did not affect the resident fish. They only increased the visit of client fish to the reef. It could be assumed that the cleaner fish used the reef as their fundamental niche and that their realized niche where they actually survive and perpetuate is somewhere closer to the fundamental niche. But their presence certainly increased competition and also predation.
This study is important to understand because it can provide us solutions to many questions such as patterns of population growth, effects of various biotic and abiotic factors on the growth of different species, species extinction and their causes, distribution patterns of various species, resource utilization, inter specific and intra specific competitions.
Life History Strategies
Life history of an organism means the events occurring right from its birth (eg, zygote and embryo), growth, development, maturity, reproduction and death. Appropriate characters used to define and analyse the life history of an individual are reproductive success, age of attaining reproductive maturity, growth period (age) and mortality rates. Life history of the individuals of a same species show great variation as the characters mentioned above also are unique to every individual. But, in general life history strategy is the average pattern of time and energy distributions that an individual makes during its growth and reproduction. When the life history of an individual is considered the amount of energy it utilizes in its growth is much higher than in reproductive efforts. But when the reproductive phase is considered and individual devotes much of its energy in the mating process.
The utility and distribution of the energy is also based on the environmental factors. If the environmental conditions are adverse for the survival of the individual, it concentrates its energy in perpetuating its race either by mating or setting seeds. Based on the way the energy is distributed in the life history of an individual, the fitness is decided. Life history strategies in most of the individuals are not designed to maximize their fitness. A successful life history should have fast reproductive maturity of an individual, successful mating, large number of offsprings which survive, short developmental phases, fast somatic growth, short period between their breeding and an effective life span. A phenomenon called Polyphenism best describes the growth of an individual in diverse environmental and nutrient challenging conditions. Eg, In cooler climates Ponderosa Pines accumulate more biomass to the leaf than those growing in warmer climates, resulting in different shapes of the tree (Callaway et al. (1994)), Body parts grow at different rates as seen in animals growing in cooler regions have thick fur coats and huge bodies when compared to the ones growing in the warmer climates. In order to have a successful reproductive rate, certain species adopt asexual mode of reproduction. But, the sexual reproduction cycles are a lot beneficial over the asexual because of recombination and variation. Complexity of the life cycle also accounts to a successful life history as larval stage and pupae consume more time over the phases like metamorphosis. I consider the choice of host by the parasites also as a criterion for a successful life history. For example, the parasite Ribeiroia (life_history_lecture) has a selection of hosts which live in a same habitat. But, it needs different hosts (Planorbella, Amphibian, bird) for it to become an adult. If during its growth, the parasite fails to reach any of the host, it dies (presence of large number of birds’ leads to predation of amphibians or due to adverse conditions the birds might migrate to another place).
r-selection and K-selection have been used to describe reproductive patterns, where r-selection is the selection for high population growth rate in uncrowded and newly distributed areas and k- selection is the selection for slower growth rates in crowded, reproductively favored regions. But, there exist problems with this sort of selection as different species have variations in mortality rates, reproductive success, and age span.
Many models have been proposed to life history strategies like the Grime’s triangular model, which distributes the individuals towards a successful growth rate based on Increasing stress, competition and distribution. Life history cube as proposed by Charnov (2002), distributes the animals based on the reproductive efforts, life span and offspring size. Trade-offs also plays a vital role in determining the life history traits. Organisms which allocate energy on useless morphological traits and functions rather than the useful reproductive features often fail to produce more offsprings and end up with limited population size.
The most commonly used definition used by most of the biologists is “A species is the basic unit of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding, producing fertile offspring and have a similarity of DNA or morphology”. http://en.wikipedia.org/wiki/Species. The working definition of a species is different for every scientist but their definitions consider at least one of the characters mentioned above. To study an ecosystem, it is important to understand specific interactions between the individuals of a species and also among the species along with the impacts of the surrounding environment. A species has various roles to play in an ecosystem such as it could carry functional importance, it could contribute significantly in a food web at a trophic level, it could itself initiate interactions among other species. Keystone species is one such category which strongly affects the other neighbouring species. A keystone species is defined as” A species that has a disproportionate effect on its environment relative to its abundance. Such species affect many other organisms in an ecosystem and help to determine the types and numbers of various others species in a community”. http://en.wikipedia.org/wiki/Keystone_species.
Keystone species are studied as they strongly influence other species. A species belonging to this category could be a predator s of another species living in the same habitat or they could lead to the increase in the population of the neighbouring species. For example, a keystone species could be a predator in a forest and preys on a species which eats trees and herbs. This leads to a drastic increase in the population of that tree or herb species.
They keystone species are further classified as the predators and the engineers. To better explain the predator keystone species consider the study by Robert Paine (1966). The sea stars are the known predators of sea urchins, mussels and various other shell fish. If this predator is removed from the habitat, the population of the mussels explodes. This is a perfect example where a species with a small population size exhibits a great impact on other species of the ecosystem. Not only causing ill effects the keystone species also act as Engineer species helping other species to grow considerably. Leakey, Richard; Roger Lewin (1999), in his paper discussed that the Elephants in the African forests play a vital role in allowing other grass species to grow, which otherwise would have been dominated by the large woody trees. The Elephants destroys these woody trees and gives space for other species to grow.
Before Darwin came up with this well known theory of The Natural Selection, naturalists believed in the biblical the theory of life and its existence. However, when Darwin published his book The Origin of Species in 1858, naturalists began to rethink about the idea of species and their evolution.
Natural selection in a species occurs and selects the best fit individuals in a species to survive and continue their existence. In order to cross natural selection, an organism has to be fit to survive any catastroph. Or it will have to have a perfect adaptations to survive and win the inter and intra specific competition.
A potentially reproducing organism, in the due course of time perpetuates and increases its population so much it would be the only dominant species on the earth. In order to suppress this process from happening and eliminating the threat of lack of habitat, resources for the other species, nature selects the best individual to survive and continue its race. I think certain instances are naturally been checked, any population in the world will always be checked by unstable environment and interaction with other plants and species. Struggle for existence is a kind of chain reaction where no organic being can go unchecked in all instances (natural).
Every individual has to overcome the struggle for existence and for this they adapt many different traits. Parents processing a successful adaptive trait will pass it on to the progeny, which makes them fit for survival. This inheritance by the next generation leads to the accumulation of higher proportion of traits which make them well adaptive and successful in survival.
In order for natural selection to occur, an individual must have a heritable trait or variation and this variation must have proved to increase the fitness. Best example to quote here is the phenomenon of Industrial Melanism. The paper by Kettlewell (1950) showed that the dark moths, Biston Betularia, are abundantly found in industrial woods whereas the light moths are more in the non industrial woods. This adaptation of body color helps these moths to survive from their predators. The moths which have successfully adapted to this change in body coloration have overcome natural selection and are fit to survive.
Hint on example from: http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html
The phenomenon of neutral theory was introduced by Motoo Kimura in the early 1970s, which talks about the evolution of a species based on the changes which occur at the molecular level. Major cause for evolution is contributed by genetic drift and neutral mutations. The neutral theory argues against the theory of natural selection by Darwin and focuses mainly on genetic drift according to Kimura (1986). When the genomes of the different species are compared we tend to find molecular differences but these differences do not affect the fitness of the organism. According to Sueoka (1962), neutral mutations are very wide spread and are a commonly occurring in every species at a same rate. I think that neutral mutations are occur at a frequent rate but are often proof read polymerases during the replication. Mutations happen to occur when an individual is exposed to an environment or during replication of DNA. According to deVisser et al. (1999) higher rates of mutations are selected for in new environments. But this is not going to affect the genotype or phenotype of an individual drastically because most of such mutations go silent or unexpressed, Kimura (1986). The probability that such mutations do not affect the individual is shown based on the degenerate genetic code. There are 2 codons GCC and GCA which code of the same amino acid alanine.
(http://en.wikipedia.org/wiki/Neutral_theory_of_molecular_evolution ). Genetic drift is also responsible of fixing an allele in a population, which ultimately becomes a commonly persisting allele in the population. This to happen in multicellular organisms mutations must occur in the germ cells and not in the somatic cells, which can ultimately be inherited by the progeny. Neutral theory can be of use if a mutation occurs in a heterozygote. For example, the presence of 2 copies of a gene that causes sickle cell anemia is harmful but, the presence on only 1 copy protects the RBC against Malaria.
Hint for example: http://evolution.berkeley.edu/evosite/evo101/IIIE6bBadgenes.shtml
1) population : 1000
PP= 640/1000 = 0.64
Pp= 320/1000 = 0.32
pp= 40/1000 = 0.04
2) number of alleles in a gene pool = 2000
PP= 640+640 = 1280
Pp = 320+320 = 640
pp = 40+40 = 80
P = 1600/2000 = 0.8
p= 400/2000 = 0.2
3) fitness of each genotype :
PP = survivors/ original = 180/640 = 0.28125
Pp = 0.9250
pp = 12/40 = 0.3
4) survived individuals
Rate of survival of
W11 = 180/640 = 0.28125
W12 = 296/320 = 0.9250
W22 = 12/40 = 0.3
Average fitness = w = p2w11+2pqw12+q2w22
= 0.1799 + 0.296 + 0.012 = 0.4879
Meso predator Release Hypothesis :
Every species plays an important role in an ecosystem and contributes to the flow of energy in the food chains/ food webs. A very recent hypothesis called the Mesopredator Release Hypothesis states that when a top predator in a food chain is eliminated (Groom, M., Meffe, G., Carroll, C. 2006), the population of the intermediate predators called the mesopredators explode in numbers causing a threat to the lower trophic levels (Palomares, E. & Caro, T.M. 1999). The top predators and the mesopredators vary based on the food chain we are looking at. This hypothesis tends to consider humans as the superior predators and the impact which they cause called the top-down control (Elmhagen, B., Rushton, S. 2007). But there are drawbacks to this hypothesis like it does not talk about the effect of lower trophic level population boom on the superior predators and also the effects of climatic conditions which play a role as a population check point. This does not also measure the before and after effects of this hypothesis on the ecosystem.
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If I had to prove this hypothesis based on an experiment, I would consider an area with numerous birds nesting on the tree tops and fence it. I would then release a non native species like a brown tree snake into the premises along with hawks. The hawks act as a top predator. The elimination of hawks from will increase the snake population, which feed on the birds and also on their eggs in the nests on the trees. This will decrease the bird population considerably in a period of time. Overtime the moth and locust population will increase as the birds which prey on them have decreased in number. The increase in the insect population will cause a huge damage to the native species like the tree which are surviving in that region. This shows that that the removal of a top predator affects the lower trophic level species drastically (here trees and bird population). To make my hypothesis even stronger I will compare the condition of the lower trophic level species before and after I release the predators into the test field.
But according to me, the elimination of a top predator is not that very important to understand the role of a certain species in the ecosystem. This is where I think the Mesopredator release hypothesis fails. In the experiment I mentioned above, the elimination of birds, which is not the top predator, increases the number of insects and hence the tree species are affected. I every species plays a unique role in the ecosystem to maintain equilibrium.
The one thing about the species concept which deQiueroz made that I agree with is
the concept that a “species is a separately evolving metapopulation lineage” and to be a species, the only requirement is for the lineage to be “evolving separately from other lineages”. However, then De Queiroz also talks about the “unified species concept”, in which he quotes that species is a diverging branch resembling a metapopulation lineage. This concept is not fair in not accepting the ‘single property’ which delineates a group of individuals from another as the criteria for naming it a new species. Without any such distinguishing properties I do not see how a new lineage is identified as a new species.
The widely accepted definition of a species is “A species is the basic unit of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding, producing fertile offspring and have a similarity of DNA or morphology”. http://en.wikipedia.org/wiki/Species. When a biologist has to talk about a species his/her definition must satisfy the above qualities. It is also true that every biologist will have a unique thought on what is a species is. For example, scientists who distinguish species based on the morphology look out for similar morphology whereas those who look out for genome similarity count on the similarities in the genomes. According to the website http://www.bcm.edu/news/item.cfm?newsID=753 genome sequencing revealed that sea urchins share a common ancestor with humans.
I think it is important to have a definition which can fit in itself most of the qualities which are required to delineate a species from the other species. I think a definition of a species should fulfil morphological similarities up to a maximum extent (eg. All the Homo sapiens are almost similar morphologically expect slight variations caused due to geographical isolations and genetic drifts), genetically the individuals of a species should have a similar genome to a maximum extent and should have a capability to interbreed and pass on the traits to the fertile progeny in order to perpetuate its population effectively.
The Lindeman paper highlights the importance of energy availing relationships among the biological communities in the ecosystems. Every biotic and abiotic factor is dependent on each other with respect to food cycles and energy cycles.
a) The Trussel et al (2006) paper discusses energy continuum and the length of the food chains as the important aspect to be considered in an ecosystem. This paper also talks about the ‘Energy- flow hypotheses and states that the length and stability of the food chains depend on the energy flow in food chain starting from a lower trophic level and proceeding towards the higher trophic level. This is quite contradictory to what other scientists thought. The energy flow from a lower trophic level to the higher trophic level determines the length of the food webs and ultimately the ecosystem size. This paper highlights some predictions like the length of the food chain also depends on the intermediate consumer brings energy acquirement and predation risk to equilibrium. The decreases in the energy flow up the food chain limits the tophic levels in a food chain.
b) Trussel conducted his experiments to show that the risk of predation in the lower trophic levels leads to less accumulation of energy in the individuals. He carried out his experiments on an intertidal food chain. The green crab was the predator and the snail was an intermediate consumer and the barnacle as the resource. The primary result obtained is that predation risk considerably reduces the energy intake in the snails and they also produced less tissue in the presence of predation risk. Predation risk reduced the energy accumulation by 31% in the snails. This shows that the presence of predators indeed affected the growth and reduced the energy acquisition in the snails. Predation risk reduced the growth of the snails at low conspecific densities indicating that when snails are present in groups, they feel less threatened by the predators.
c) In this paper Trussel summarizes his results that at higher conspecific densities lead to higher growth efficiency than at low conspecific densities in the presence as well as the absence of the predator. They hint that the physiological stress caused in snails is higher in low conspecific density in the presence of a predator which leads to the decreased tissue production in the snails. Low conspecific density creates high environmental risk for the snail in the presence of the predator. In the absence of predators, high conspecific density leads to high tissue formation and efficient growth. I think there existed intraspecific competition, between the individuals for resources. In order to ingest more resources the fittest snails which are bigger in size must have moved towards the barnacles and fed faster to increase in body mass and tissue production whereas the weaker snails fall prey to the crabs as they could not overcome physiological stress and compete for resources. Although the energy accumulation was low in the high densities, the growth was considerably more when compared to the low densities. But in the presence of the predators there was no evidence of competition as snails acquired more energy when in low densities.
10) A potentially reproducing organism, in the due course of time perpetuates and increases its population so much it would be the only dominant species on the earth. In order to suppress this process from happening and eliminating the threat of lack of habitat, resources for the other species, nature selects the best individual to survive and continue its race. I think certain instances are naturally been checked, any population in the world will always be checked by unstable environment and interaction with other plants and species. Struggle for existence is a kind of chain reaction where no organic being can go unchecked in all instances (natural). Natural selection in a species occurs and selects the best fit individuals in a species to survive and continue their existence. It is process of developing well suited adaptations which increase the fitness of an individual. Adaptations can occur in order to cope up with the environmental conditions or due to mutations or due to genetic drift. Nature selects individuals with the best adaptations which can overcome all the selective pressures. Such traits and adaptations become fixed in an individual in due course of time. During reproduction these traits are inherited by the progeny. Reliable traits get fixed in the individuals in the due course of time. Hence after several generations of successful mating and production of offsprings, the trait gets fixed in a population. Natural selection starts in an individual but continues until an adaptation is fixed in the entire population. By chance if a trait which is of no use is fixed in the individuals, they cannot survive longer due to the naturally acting selective pressures. For example, if pollen, which is used for perpetuating most of the plant species is light weighing and attractive with tools for pollinating mechanism like wings (easier through air dispersal and also attractive pollen attracts birds and animals), it is adapted and fixed in that entire plant population. But if it has bad odour and is heavy, the plant could get extinct as the pollen is not dispersed to faraway places and accumulated growth could lead to intraspecific competition and also natural calamities could destroy them.
“Is it the gene, the genome or the organism that evolves?” Well I think that the genes evolve first. It can occur due to random mutations. These mutations are usually deletions or insertions and most of the times go unnoticed and unexpressed. Genetic drift causes these gene variants to vanish. http://www.nature.com/hdy/journal/v100/n2/full/6801000a.html. The mutation in the gene may not lead to an evolution of the complete genome as the Neutral theory also acts on the random mutations. Most of the DNA is non coding and represented as introns which are ultimately spliced during translation and there are minute chances of a functional gene getting mutated and expressed in spite of the proof reading enzymes acting upon them. So, if a genetic evolution has to occur, changes should be incorporated into the regions which regulate the gene expression.
Natural selection is a directional procedure which happens taking into account various inter specific and intra specific interactions giving rise to adaptive traits whereas genetic drift occurs randomly, which halts the trait fixation in a population, reducing the genetic variability.
Hint on the topic: http://www.physicsforums.com/archive/index.php/t-170122.html
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