Answer:
Those species that are more vulnerable to extinction are the big-sized ones, that reach their sexual maturity in a relatively advanced stage of their lives and have a low growth rate per capita. They have a low reproductive rate.
Explanation:
There are specific heritable traits such as reproductive rate, trophic level, dispersion capability, that influence different species and their trend to be more or less vulnerable to extinction. "k" species have a low growth rate per capita, but they are big competitors with the capacity of displacing other species and monopolizing the available resources. These are big-sized species that live for a long time, reaching sexual maturity in advanced stages of their lives. They do not have numerous progenies, and hence, they spend a lot of time in parenting. Any environmental disturbance seems to severely affect them. These animals have a higher risk of getting extinct than those species with short-lived and elevated reproductive rates.
For many mammals and birds, this is a linear relationship. The bigger is the species, the more prone to get extinct it is.