Phenotypic variations among individuals within the populations can result in differences in the nature and degree of interactions that occur.

Classification 12.1

By designating the positive effect of one species on another as +, a detrimental effect as −, and no effect as 0, we can develop a classification of possible interactions between two co-occurring species: (00) neutral; (0+) commensalism; (++) mutualism; (0−) amensalism; (−−) competition; (+−) predation, parasitism, or parasitoidism.

Population Dynamics 12.2

Species interactions typically involve the interaction of individual organisms within the respective populations. By influencing individuals’ probabilities of survival or reproduction, interactions influence the collective properties of birth and death at the population level, and in doing so, influence the dynamics of the respective populations.

Natural Selection 12.3

Phenotypic variations among individuals within the populations can result in differences in the nature and degree of interactions that occur. These phenotypic differences may influence the relative fitness of individuals within the populations in the degree of interaction, resulting in the process of natural selection. The process in which two species undergo reciprocal evolutionary change through natural selection is called coevolution. Mutually beneficial interactions typically serve to reinforce the phenotypic changes that result from the species interaction, and mutually detrimental interactions typically result in phenotypic changes that function to reduce the intensity of interaction.

Geographic Variation 12.4

Species with wide geographic distributions are more likely to encounter a broader range of biotic interactions. Changes in the nature of biotic interactions across a species’ geographic range can result in different selective pressures and adaptations to the local biotic environment. Ultimately, differences in the types of species interactions encountered by different local populations can result in genetic differentiation and the evolution of local ecotypes.

Diffuse Interactions 12.5

Most interactions are not exclusive involving only two species but rather involve a number of species that form diffuse associations.

Niche 12.6

The range of physical and chemical conditions under which a species can persist and the array of essential resources it uses define its ecological niche. The ecological niche of a species in the absence of interactions with other species is referred to as the fundamental niche. The species’ realized niche is its ecological niche as modified by its interactions with other species within the community. Species interactions can function to either restrict or expand the fundamental niche of a species dependent on whether the interaction is detrimental or beneficial.

Adaptive Radiation 12.7

Variations among local populations in biotic interactions can result in phenotypic divergence and therefore have the potential to function as mechanisms of adaptive radiation, if the divergence in phenotypic characteristics results in reproductive isolation.

Urban Ecology Ecological Issues & Applications

Urban ecology is the study of the ecology of organisms in the context of the urban environment. Increased urbanization has led to a decline in habitat and loss of many native species, while providing habitat for other, often non-native species.

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