An ecologist samples the abundance of various species along an environmental gradient and fails to find clusters of species. Instead, peaks of abundance of dominant species are merely randomly spaced segments along a continuum. This distribution of species supports the

This distribution of species supports Gleason´s Individualistic concept of a community.

Explanation:

This theory was proposed by Gleason and it states that plant species respond individually to environmental factors that continuously change at spatial and temporal levels. This means that the combination and distribution of plants in a certain point or area are unique because each vegetable species has a different distribution pattern and a different tolerance and abundance rate. Hence each species´ response curve to a certain gradient has its own shape and size and it different from other species curves.  

Plants assembly growing in an area is the result of environmental conditions and migration rate of species. As every area is continuously getting propagules of different species, the survival success of each plant depends not only in environmental factors, but also depends on the tolerance to other new species and their interactions. This combination along a gradient always results in different composition and abundance of species. This is why a sample can not be confined to a clearly defined vegetable community.

This point of view is known as individualistic or continuum concept of vegetable community. Gleason believed that vegetable species were distributed as a continuum and that communities can not be identified as combinations of associated species that repeat in space.

answer: a. a gene that causes a specific trait.