Ecological succession is the natural process, which, after some environmental disruptive disturbance, gradually replaces the communities of organisms by other individual communities that fit basically the same role. This is not much unlike how commercial enterprises tend to fire only a handful of employees at a time such that the entire worker-knowledge-base is not lost, such that operations can continue. One example of ecological succession is the local drought and populations of water-dwelling creatures. As the water levels go down, the available resources and living spaces decrease as well. Once our drought ends, larger populations will be supportable. Each of the communities, in the mean time, has been replaced by growing communities that better fit into the same place in the trophic pyramidic system. It is possible that through the drought the area becomes a meadow, and the meadow then develops into a forest over time—this is, of course, assuming that some geological process prevented the lake or stream from reforming into the water body that it once was. The change only occurs with the support of populations of organisms doing their individual things to keep alive. The pioneering communities transform the newly developing environment and pave the way for other organisms to contribute, for example, before deeply rooted plants can develop there has to be a contribution of soil, and thus perhaps first dirt and grass on the surface for livestock to graze and then produce droppings that would add up over time and provide for the climax or stable community as a part of secondary succession.
The trophic levels involve the chain through which energy flows in an environment. The primary producers (autotrophs) are able to convert inorganic (chemical) energy and sunlight into usable organic (biotic) energy. The primary consumers eat the autotrophs and attain some but not all of the energy that the autotroph was able to obtain. Secondary and tertiary consumers can then eat the other consumers and then the top consumer gets only the smallest percentage of the original amount of energy. This turns out to be the second law of thermodynamics, which states that entropy increases with respect to time, and can be explained by the fact that it takes energy to access energy, and that there's no way to absolutely perfectly store energy (for that would take energy to keep the energy from dissipating). One example of a (small) trophic pyramid would be a small forest. In this forest, the grass and trees are the autotrophic organisms, and the rats eat the grass. The rats are considered consumers. The wild gang of originally domesticated cats play the role of carnivore and eat the rats, thereby attaining the organic energy originally from the sunlight. The top consumer is then, say, the community of owls that swoop down to take cats as prey. In that example, the owls would receive the least percentage of the original amount of energy. Given any increase or decrease in the population of the lower-level consumers or producers, the top consumer population can vary as well (although there may be internal moderation factors embedded into the genome to keep the top predators from eating everything else and thus killing off sources of energy, food, etc.). The productivity of an ecosystem could be used to talk about the amount of energy converted from radiation (from the local star) to chemical to kinetic energy in the ecosystem. For example, only a certain amount of energy is eventually used for biological gains—not all organic energy is completely used and thus why we see flesh rotting on dead animals, although many microscopic and scopic organisms show up on the scene to take as much as possible (fungi, vulchers, etc.).
Liebig's law (from the 1840s) states that the growth of a population is not dependent on the most abundant resource but rather the most limited resource. This law is also known as the law of minimums. Liebig noticed that if you looked at a population of, say, animals, that the growth of the population is not necessarily dependent on the amount of resources available in the summer but rather through the time of greater adversity—during the winter. This correlates with numerous historical examples. One particularly vivid example is the human populations as they migrated from European countries to North America and established various charter cities from their alpha males back in Europe. The new colonies may have had an abundance of resources during the summer, but many barely survived through the winters. The colony of Jamestown is one of those particular cases. Density independent factors change the birth and death rate regardless of population density. Density dependent factors, however, change relative to population density. The abiotic factors are those of the physical environment like temperature, geological events and cycles, weather, climate, humidity, soil, sunlight, etc. (even though soil is commonly fertilized by biological processes).
Carrying capacity is the point at which the birth rate and death rate are equal to each other. Carrying capacity is also, more generally, the number of organisms that the environment can support. The carrying capacity of a population is determined by the limiting factors of the environment. The point at which birth rates and death rates are equal is a stabilized population density, or a stabilized number of the total number of organisms of the population with respect to some area. Varying population size means varying rates of death or birth with what is normally a static carrying capacity. Granted, the carrying capacity of an environment need not remain the same—perhaps by the growth of grass there can be more members of an elephant population (just a simple example).
The energy flow through a specific ecosystem can accumulate biomass at specific levels of the trophic system. Biomass is defined as biotic compounds. The available biomass is like a big giant battery pack, although it has to be specifically organized in order to be accessible to the populations in the environment. The accumulation of biomass provides for the development of more populations and even the introduction of further species. New relationships can develop in the areas where there is available biomass that is going unused. For example, animal droppings provide an environment for dung beetles.
Ecological succession:
the natural process, following a disturbance, in which one community of plants and animals gradually replaces another, in response to changing environmental conditions.
Process in which communities of plant and animal species in a particular area are replaced over time by a series of different communities.
`Ecological succession, a fundamental concept in ecology, refers to more-or-less predictable and orderly changes in the composition or structure of an ecological community. Succession may be initiated either by formation of new, unoccupied habitat (e.g., a lava flow or a severe landslide) or by some form of disturbance (e.g. fire, severe windthrow, logging) of an existing community. The former case is often referred to as primary succession, the latter as secondary succession.`
`The trajectory of ecological change can be influenced by site conditions, by the interactions of the species present, and by more stochastic factors such as availability of colonists or seeds, or weather conditions at the time of disturbance. Some of these factors contribute to predictability of successional dynamics; others add more probabilistic elements. In general, communities in early succession will be dominated by fast-growing, well-dispersed species (opportunist, fugitive, or r-selected life-histories). As succession proceeds, these species will tend to be replaced by more competitive (k-selected) species.`
` "Ecological succession" is the observed process of change in the species structure of an ecological community over time. Within any community some species may become less abundant over some time interval, or they may even vanish from the ecosystem altogether. Similarly, over some time interval, other species within the community may become more abundant, or new species may even invade into the community from adjacent ecosystems. This observed change over time in what is living in a particular ecosystem is "ecological succession".`
` In order for an ecosystem to go through succession, the organisms in each wave of succession must be available in the local environment`
` The farther an ecosystem is from a source of these organisms, the less likely these organisms will be present and therefore that succession will occur`
The hypothesis of island biogeography
` (a) One thing that limits the carrying capacity for many organisms is that the presence of these organisms essentially spoils the environment for their continued presence`
` (b) Such organisms typically are r-selected, and essentially are good at finding environments they can exploit, exploiting those environments, then giving way to organisms which are better at hanging on in those environments
(c) The exploitation of an environment by one population, followed by the exploitation by a second (third, etc.) population is termed ecological succession
(d) "Many of the changes in community structure during succession may be induced by the organisms themselves. Direct biotic interactions may be involved, including inhibition of some species by others through exploitative competition, interference competition, or both. The presence of organisms also affects the abiotic environment by modifying local conditions. This may result in facilitation, in which the group of organisms representing one stage 'paves the way' for species typical of the next stage . . . Sometimes the changes that facilitate the development of a later stage actually make the environments unsuitable for the very species responsible for the changes."
Ecological succession continues in a habitat until species, typically K-selected, that are good at nurturing their young within the same environment (as well as good at excluding other species) comes to dominate the environment, or until catastrophic change essentially wipes the slate clean, making an environment once again exploitable to the r-selected populations`
Distinguish between primary succession, secondary succession, and a climax community.
` (39) Primary succession
(a) Ecological succession typically occurs in fairly well-defined waves of succeeding organisms
(b) When the environment being exploited is essentially lifeless—lacking in both living organisms and in their remains—then the first round of exploitation is termed primary succession
(c) Primary succession occurs, for example, following volcanic or glacial destruction of an environment
(d) The first organisms that exploit an otherwise lifeless terrain are termed primary successors
(e) Primary succession is a fairly rare occurrence especially relative to the much-more familiar secondary succession that we observe in disturbed habitats all around us
[primary succession (Google Search)] [index]`
` (40) Secondary succession
(a) Secondary succession is succession that follows primary succession, i.e., of an environment that already contains life (or, at least, soil)
(b) "Because resource availability changes over the course of succession, different species compete better at different stages. Early stages are typically characterized by r-selected species that are good colonizers because of their high fecundity and excellent dispersal mechanisms. Many of these may be described as `fugitive' or `weedy' species that do not compete well in established communities, but maintain themselves by constantly colonizing newly disturbed areas before better competitors can become established in the same places."
[secondary succession (Google Search)] [index]`
Answer each of these as completely as possible. Cite resources as necessary. Refer to the University of Georgia web site to garner preliminary grading information.
Using an example for each, discuss the following ecological concepts.
Succession
Energy flow between trophic levels
Limiting factors
Carrying capacity
Describe the process of ecological succession from a pioneer community to a climax community. Include in your answer a discussion of species diversity and interactions, accumulation of biomass, and energy flow.
This will be due a week from today which would be .. October 17th. The evolutionary objectives are due on Oct. 12th, the AP lab is due Thursday or maybe Oct. 13th.
Bryan Bishop Ecology Free Response October, 02006
Due Oct. 17th