The dimension of patches has inherent related consequences. A small patch means a population of small dimension with greater external influence reaching the inner parts.
We know that small animals have higher exchanges with the external medium. For instance, a hummingbird or a firecrest (Regulus sp.) has to spend more energy to maintain internal homeostasis than an elephant. The same mechanism is active in small patches that become sensitive to external influence.
For instance, small patches of shrubs are more easily burned than large ones because of the surrounding invasive highly inflammable grasses. So the persistence of small patches is less certain than large ones. In some cases, small patches can survive better than large ones if a disturbance regime is acting against it. For instance, along a tree fall on steep mountains small patches of vegetation have less probability to be intercepted by rock outcrop, but this is only an example of a specific situation; the opposite is the rule. From an organismic perspective a small patch may not be enough to host a species, or only a limited number of individuals can be supported. Again in this case a reduced population of hosts can be supported, or only a few parts of a habitat patch can be considered source.
Some species are particularly sensitive to the border of suitable habitats and for this reason need a large extension of "habitat" far from this border. These species have been called "interior" species. The internal part of this habitat is called the "core area." In theory, two hypotheses can be presented: The first is that at the border of a habitat there is no "habitat" for that species, and the second hypothesis is that a less suitable habitat is placed at the periphery and that this habitat is populated only by sink populations that survive only by the refueling of individuals lost by new arrivals from source habitats.
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