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2005
Conservation biology
Conservation Biology Report
Any ecological community existing on earth goes through several changes over time, replacing species within the community. This phenomenon is known as succession, in which primary succession occurs from a site with no occupation by a community, and secondary succession occurs from a site where an existing community was once removed. There are three main models considered by Connell and Slatyer (1977) explaining succession procedures; facilitation, tolerance, and inhibition pathways. Since each model captures a different aspect of succession, all three models are not necessarily conflicting models. The first common condition among all three models is that disturbance occurs causing a relatively large open space, in which resource is released. The succeeding process in which species behave differently determines the separate pathways.
Firstly, the facilitation model shows a positive effect towards the early stages of succession. The alteration of environmental conditions and resource availability creates a more suitable environment for later species, allowing later successional species to establish in that site. Out of all the species that arrive to the open site, only specific species specializing in early succession are capable of establishing in the site at first. Their establishment in result changes the environment less suitable for early species, allowing species of late succession to establish instead. Replacement of species occurs at this stage by modifying the environment so that early species facilitate the growth of later species to maturity, and eliminating earlier species in exchange. Facilitation model is thought to fit best in primary successions, where pioneer species establish in harsh earlier phases of succession, and thus demonstrates the well-known succession sequence. On the contrary, the other two models mentioned later on, have been tested in later species-rich stages. Connell and Slatyer regard the question of stability, in which succession is a balancing reaction which occurs in a stable system when disturbed. Only certain early species of succession are able to establish, dominate and modify the environment. This succession sequence continues until the residing species no longer largely modifies the environment for facilitation to occur for other species to invade and grow.
Secondly, the tolerance model explains how juveniles of many species establish in the early succession stages according to its growth rate and interspecific competition. Species tolerant to the environment at this stage would persist to survive. As obvious, this model would include climax species as being present at the earlier stages of succession, being a subset of the early species and further surviving throughout succession. Later species, therefore, are successful whether earlier species have preceded establishment or not, signifying that the conditions produced by earlier species, required in the facilitation model, are unnecessary or do not affect later species. As the succession sequence proceeds, the environment becomes less suitable for the recruitment of early species of succession, in which the change in environment has very little or no effect upon late species. This results in the growth of late successional species regardless of the presence of early species, eliminating earlier species. The tolerance model would continue the succession sequence until the restricted site can no longer be invaded. The sequence of species replacements result from different species having different strategies in resource usage, i.e. later species are tolerable to low resource levels than early species and can outcompete them and grow to maturity. In these two models of facilitation and tolerance, early species are displaced by later species due to competition among resources such as light and nutrients with the newcomers. The tolerance model states the appearance of both early and late species at the first stage after disturbance has occurs. The growth of the pioneer species, creating shade, allows less availability in resource for early-stage succession species (intolerant to shade). Little or no effect, however, is to be seen in those that are tolerant to shade (i.e. later species).
Lastly, the inhibition model is often defined as being the opposite model of the facilitation model. In inhibition, establishing species earlier in the successional stage would inhibit subsequent species from establishing and further grow to maturity in the same community. Similar to the tolerance model, any species that arrive to an open site are able to survive and establish themselves as adults in that site. Due to early occupants in the site, the environment becomes less suitable for both early and later succession species. The earlier colonists would thus exclude or inhibit the invasion of subsequent colonists under the conditions that the earlier species are undamaged and continuingly regenerating. Disturbance, however, continues to occur over time. In this model, later species of succession would establish in the community when earlier species are disturbed by severe conditions or predators once again. This model would only account for situations when disturbance persistently exists, where later species replace earlier ones by physical conditions, unlike the former two models affected by resource conditions. In these three models explaining succession, it is important to consider the fact that earlier species are not able to invade, establish, and grow once the site is occupied. Species following the tolerance “pathway” would not be able to establish in a site if there were not enough room. Competition continually exists over time and species that are able to use resources most efficiently succeed and outcompete with others. The first-invading species inhibit growth and development of other species subsequent in succession, resulting in a type of incorporation between early and delayed succession species. Studies testing these proposing models of Connell and Slatyer have been made for the interference of succession mechanisms by removing species, sowing seeds and planting seedlings. The main objective of the proposal of these models was to suggest types of succession mechanisms that work between species in a certain forest.
As can be seen, different succession sequences support all three models. However, as each model being unique in its own way, it can be said that all three models are supported at only a particular stage. In other words, the entire succession sequence and patterns cannot be fully explained by one single model; i.e. facilitation is not the only process that underlies succession (facilitation does not always occur or is required for the establishment of later species or for the succession sequence in some cases). These three models therefore are not necessarily opposing models; a certain species would not necessarily undergo one type of succession sequence throughout its life history.
Results showing that both facilitation and inhibition occur in a succession sequence have been reported. These two "pathways" may not coexist at the same stage, but would be capable of occurring at different stages of the life cycle of invading species. The same can be said between the facilitation and tolerance model. In an experimental study of succession on Mount St. Helens, a perennial lupine Lupinus lepidus was examined for its effects on two common colonists (Anaphalis margaritacea and Epilobium angustifolium) of the Pumice Plains in Mount St. Helens. Lupine, being a nitrogen-fixing legume, was expected to facilitate the establishment of other species colonies, increasing the levels of nitrate, and also for its capability to supply shade in environmental conditions of high surface temperature and low moisture. Inhibitory effects of lupine were at the same time also expected, as large lupine patches only persisted in monocultures and because the spatial distributions of the two main colonists (Anaphalis margaritacea and Epilobium angustifolium) did not correlate with that of lupines. As a result, it was shown that Lupinus lepidus performed a combination of beneficial and disadvantageous effects (i.e. facilitative and inhibitory) on the establishment of the two common species of the Pumice Plains. This supports the proposal that a balance of facilitative and inhibitory effects exists in the influence of early species on later invading species. Depending on perspectives, the mechanisms of facilitation and inhibition act on different stages of the life history of succession species (i.e. inhibitory effects on seedling survival, while facilitative effects are observed in seedling growth of A. margaritacea and E. angustifolium in lupine patches). Similar results were seen in woody plant establishment in abandoned agricultural fields of New York. Different species at different life stages, supported all three of the succession models; the facilitation model being supported in increased seedling emergences and survivorship with herbs existing, tolerance seen in some cases of seed predation and seedling emergence, and the inhibition model supported in cases of decreased growth and survival of seeds and seedlings in the presence of herbs in the state of environmental stress.
As shown, the three models proposed by Connell and Slatyer are not conflicting hypotheses, but simply a classification of different possible outcomes which may occur at different circumstances. The three mechanisms of succession, facilitation, tolerance, and inhibition, do not oppose one another because of its capability to act on different stages of the life history of species in the community within the succession sequence.
References
- Crawley, M. Plant Ecology. Blackwell Science 1997.
- Schulze, E.D., Beck,E. and Muller-Hohenstein K. Plant Ecology. Springer 2005.
- Finegan, B. 1984. Forest succession. Nature 312:109-114
- Gill, D.S. and Marks, P.L. 1991. Tree and shrub seedling colonization of old fields in central New York. Ecological Monographs 61(2):183-205
- McCook, L.J. 1994. Understanding ecological community succession: causal models and theories, a review. Vegetatio 110:115-147
- Morris, W.F. and Wood, D.M. 1989. The role of lupine in succession on Mount St. Helens: facilitation or inhibition? Ecology 70(3):697-703
- Pickett, S.T.A. Collins, S.L. and Armesto, J.J. 1987. A hierarchical consideration of causes and mechanisms of succession. Vegetatio 69: 109-114
2001
Submitted to: Advanced Course in Regional Planning II
QUIZ I: Plant Community that makes below-ground competition more than above-ground competition.
In general, plants are likely to compete for three kinds of essential resource photosynthetically active radiation (PAR), water, and essential nutrients. Results from some studies have conclusion that belowground adult-juvenile competition is little or no importance for seedling regeneration. However, three line of evident and one piece of theory suggest that release from below-ground competition for nutrients may increase seedling growth and survival rates: field trenching experiments, pot experiments, field observations, and optimal foraging theory.
Below-ground competition have significant effect if plants growing on a community with nutrient-poor soil but not on nutrient-rich soil. This is suggested that, on nutrient-poor soil, seedling are competing with adult trees for nutrient as well as PAR, or root of plant competition in uptake water or nutrients was very high. The other experiments shown that many plant species can increase growth rates with nutrient additions.
One example of plant community with nutrient-poor soil is forest or green plant community in the dry-land ecosystem. In this community the light and carbondixide may be enough for their requirements. However, their requirements for water and soil nutrient are nor available. Therefore above-ground competition for light, and carbondioxide are not high, however below-ground competition is too hard because soil poor in water and nutrient contain. As we known that water and nutrient are important factor for physiological process in plant growth.
Water is needed in the photosynthesis process. Water deficiency has direct effect on plant metabolism. In photosynthesis water storage affects carbon dioxide supply, the photochemical reactions which combine water and carbon dioxide, the chemical reduction and the translocation of photosynthates. Therefore in this community, below-ground competitive more than above-ground competition.
QUIZ II. Any herbivores in the field and their effects on plant growth (In this quiz I would like to explain about effect of any herbivores to the plant based on information that I get from some paper).
Herbivores have played and affect to the plant growth. Some studies shown this role. For examples: defoliation by herbivores is among the main factors limiting plant growth. Defoliation may lead to carbon accumulation if it remove a substantial part of nutrient reserves of a plant growing in a nutrient poor soil. Herbivores significantly affected floral trait and female fitness of plant.
1. Mollusc (Helix aspersa, Capaea hortensis, and Arianta arbustorum), and aphid species (Sitobion avenae) on 24 grassland plant species.Herbivory had significant and large effect on above-ground biomass after growing season. Invertebrate herbivores (in moderate and high soil fertility)fed selectively on early successional, fast- growing species, thus increasing the relative abundance of later successional, slow-growing species. This support that herbivory increases the rate secondary succession. Flowering and viable seed production of early successional ephemerals was also reduced by invertebrate herbivores across a wide range soil fertility.
2．Vertebrate herbivores : large and small mammal (rabbit) on Trientalis europeae
The effects of herbivory on standing biomasss were dramatic, significantly reducing above-ground biomass/production and expansion of the root zone. Above-ground biomass, below-ground production, soil elevation and expansion of the root zone decreased due to herbivore activity.Vertebrate grazers (mainly small rodent) feed on young shoot of Trientalis europaea in the spring. Vertebrate grazing affected all phases of the pseudo-annual life cycle of T. europaea. Grazing prevented flowering and fruiting, increased ramet mortality during summer and decreased tuber production. Futhermore, grazes ramets produced shorter stolonsand smaller tubers, which in turn had a lower winter survival and produced smaller ramets in the following growing season. The larger impact of grazing was due to the consumption of the whole of the single shoot of ramets of T. europaea. Althought regrowth was possible, secondary shoots were significantly smaller and assimilation was delayed.
III. Environmental factor that greatly influences plant community structure.
There are two factors that influence plant community structure: the abiotic factor (non-living) and the biotic factor (living). Examples of abiotic factors which affect to plants are temperature,, light, soil structure, water and nutrient supply. The biotic factors includes genetic potential and variation within species, plant/animal interaction, plant competition, mutualism and paratism. Each factor has influence specifically, and collectively determine plant community structure.
However, the greatly environmental factor that great influences plant community structure is light. Because the quality and quantity of light affects plant growth and development, and almost community are green plant. Visible light is essential to all green plants as the energy source for photosynthesis; infra-red and far-blue radiations play an important role in photoperiodism, and ultra-violet radiations, however, can be harmful to living organism.
The light requirements of different plan species result in the development of complex stratified communities. Green plant vary in their requirement for light and many species have morphological and phyological adaptations which maximise their growth efficiency under different light intensity. Morphological and physiological adaptation of plant influence plant community structure. Therefore light is a greatly factors that influence plant community structure.
References:
- Daubenmire, R.F. 1974. Plant and Environment. Third Edition. Wiley Intenational edition. 422 p.
- Ford, M.A. and James B.G. 1998. Effects of vertebrate herbivores on soil. Processes, plant biomass, litter accumulation and soil elevation changes. In a coastal marsh. Journal of Ecology . 65: 974-982.
- Fraser, L.H. and Philip, G. 1999. Interacting effects of Herbivory and fertility on a synthesized plant community. Journal of Ecology. British Ecological Sociaty. 87: 514-525.
- Lewis, S.L. and Edmund V.J.T. 2000. Effects of Above- and belowground Competition on Growth and Survival of Rainforest tree Seedling. Ecology 8 (9). Pp. 2525-2538.
- Rieley, J. and Page, S. 1990. Ecology of plant community. A physiological account of the British vegetation. Longman Scientific & Technical. John wiley & Sons, Inc. New York. 177 p.
English