I have a test where I am given the following article, what is an answer for the question: What is P.g. holboelli twice as numerous as? ?

The red-necked grebe has a large range, estimated at 1–10 million square kilometres (0.4–3.8 million square miles), and a global population of 150,000–370,000 individuals, with P. g. holboellii about twice as numerous as the nominate race. The population trend has not been quantified, but it is not believed to meet the thresholds for the population decline criterion (declining more than 30% in ten years or three generations) of the IUCN Red List. For these reasons, the species is evaluated as Least Concern.The red-necked grebe is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies. Parties to the Agreement are required to engage in a wide range of conservation strategies which are describes in a detailed action plan. The plan is intended to address key issues such as species and habitat conservation, management of human activities, research, education, and implementation.The Red-necked Grebe was hunted by humans in northern Europe in the Mesolithic and Paleolithic periods, but there is no evidence that there is any significant level of hunting at the present time. In North America, there are potential threats from pollutants such as polychlorinated biphenyls (PCBs) and pesticides such as DDT which cause reduced reproductive success due to egg sterility and eggshell thinning. Breeding areas may be threatened by the modification and degradation of lakes and by human disturbance from water-based recreational activities. There is no evidence to suggest that these threats could result in a significant risk to the overall population; more than 70% of North American red-necked grebes breed in Canada, where the population is stable or increasing.

red-necked grebe