Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species because of differences in color patterns of the feathers and size of the beak. Recently these birds have been reclassified as eastern and western forms of a single species, the yellow-rumped warbler, based on the observation that the two forms interbreed often in nature and the offspring have good survival and reproduction. The earlier classification into two species was using a species concept; the reclassification is using the species concept.

morphological; biological

Explanation:

The morphological species concept highlights the importance of physical traits to delimit species. This concept is useful for classifying asexually-reproducing organisms and where lack information on interbreeding (for example, to classify fossils). On the other hand, the biological species concept states that one species represent a group of organisms that can interbreed (or potentially can interbreed) in order to produce fertile offspring. The biological species concept is nowadays the most widely accepted concept to define species.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!