Source Sink Model and Eco Field

The source-sink model demonstrates how a consistent immigration of individuals from a healthy population may allow a species to perpetuate in a habitat that would otherwise drive the population to extinction (Pulliam 1988, 1996).

Consequently, simple population measures, such as bird abundance during the breeding season, must be associated with a ratio of survival to mortality that is greater than one to be considered robust indicators of habitat suitability.

Outside the breeding season the factors that drive species to select habitats that could have source-sink-like dynamics remain largely unknown.

Some habitats are very attractive for animals but often they are true ecological traps and definitively sink habitats. Animals de facto are deceived by semiotic interfaces that emit a "green light" for a specific habitat. The habitat suitability is decided by an individual on the basis of a specific spatial configuration coupled to a structural configuration. The semiotic process may surprise and force the wrong decision. The tradeoff/integration between the eco-fields remains the major agent of habitat selection, but it's the distribution and abundance of resources that probably drive such source-sink dynamics. The presence or absence of a specific resource like food is discovered only after the "decision" to stay in a place, but after this choice it becomes too late for a species to change "address" and if resources are scarce the risk of local extinction becomes high.

The eco-field hypothesis seems very useful to describe source-sink dynamics because an individual that selects a "sink" habitat does not make a mistake but is deceived by a multiplicity of favorable conditions that remain largely unverified before habitat selection. Each eco-field is acting as an interface between needs and resources, but to couple the needs with resources requires for every organism to experience the structure of that specific eco-field. This means that an individual could stay in a specific place with or without resources. If the second hypothesis is realized the life trait connection with that specific eco-field would be damaged.

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