Dispersal of seeds strictly by gravity should not overlook storm effects: seeds from a deteriorating cone growing high on a tall, narrow tree will get spread widely during a wind storm.Įncasing seeds in a rounded fruit promotes gravity driven movement away from the parent.
#DISPERSIO PATTERS OF OF ORGAISMS FULL#
Most extant conifers are long-lived large shrubs or tall trees, thus taking full advantage of gravitational dispersal and allowing for gradual up slope movement of a population. The naked seeds of gymnosperms are largely dependent upon gravity for dispersal. Gravity may be sufficient agent for plants growing on steep slopes, but upslope movement of a population can be a problem. Spores, being much lighter, are more influenced by physical movements in the environment, especially those of wind (" anemochory") and water, and therefore less strictly subject to the simple motion of gravity (see examples below). Heavier seeds will tend to drop downward from the parent plant, and not very far by themselves. The effect of gravity on the dispersal of seeds and spores is straightforward. Indeed, in many instances of plants introduced into areas where they are not native, it is the failure of the dispersal mechanism that accounts for the species not becoming established beyond the garden. However, realize that particularly where plant-animal interactions are central to the dispersal mechanism, seeing a plant outside of its native ecosystem may not reveal so much about the adaptations present in the fruit and seed. Examine the fruit of any species and it is likely, with perhaps a bit more knowledge about the ecosystem, to at least intelligently speculate on what these adaptations are in that plant. Those properties or attributes that promote the movement of the next generation away from the parent plant may involve the fruit more so than the seeds themselves.ĭispersal is a universal biological need, and it is to be expected that most higher plants have solved the problem in one way or another through adaptations involving their fruit or seed. Consequently, plants have evolved many ways to disperse and spread a population through their seeds or spores (see also vegetative reproduction). Unlike animals, plants are limited in their ability to seek out favorable conditions for life and growth. In most cases, organisms (plants and especially sedentary animals) have evolved adaptations for dispersal that take advantage of various forms of kinetic energy occurring naturally in the environment: water flow, wind, falling (response to gravity).ĭispersal of organisms is a critical process for understanding both geographic isolation in evolution and the broad patterns of current geographic distributions. More significantly, dispersal enables the species population to occupy much of the available habitat, thereby maximizing resources in its favor and providing a hedge against local adverse events.
In the latter case, dispersal may simply involve replacement of the parent generation by the new generation, with only minor changes in geographic area occupied. Dispersal relieves pressure for resources in an ecosystem, and competition for these resources may be a selection factor for dispersal mechanisms. This is necessary for members of a population because organisms of the same age require all of the same resources within an ecosystem. Dispersal implies movement-movement away from an existing population (population expansion) or away from the parent organism (population maintenance). Biological dispersal refers to those processes by which a species maintains or expands the distribution of a population.
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