The main reason is they don't want species of animals to be annihilated.
They are assigned by biologists.
Biologists classify animals by their body structure, the way their body structure develops, and by their DNA.
65.000 dollars...
Biologists particularly zoologists
Animal Precinct - 2001 Tracking the Truth was released on: USA: 5 June 2006
Animal Atlas - 2004 Animal Populations 8-7 was released on: USA: 24 October 2011
A lot.
Trees
Larry M. Hunt has written: 'Energy flow in animal populations' -- subject(s): Animal populations
Sometimes only if you need to know how the animal died.
- Cell biologists: Study animal cells and their functions - Ecologists: Study animals and their interactions with their environments and humans. - Conservation biologists: Control and manage animal populations and their habitats. - Physiologists: Study how animals function and how they are adapted to live in their environments. - Systematists: Study evolutionary relationships between living and fossil animals and categorise animals. - Palaeontologists: Study evolutionary relationships between fossil animals - Taxonomists: Discover and describe new species or animal groups. - Entomologists: Study insects. Some study the roles and control of insect pests. - Herpetologists: Study amphibians and reptiles - Ornithologists: Study birds - Mammalogists: Study mammals - Parasitologists: Study parasites - Epidemiologists: Study the spread of diseases. - Ethologists: Study animal behaviour - Ichthyologists, Fisheries biologists: Study fish, fish populations and ways of growing fish and other aquatic animals - Aquaculturists: Study fish populations and ways of growing fish for commercial use. - Geneticists: Study the genetics of animals - Developmental biologists: Study the genetics of animals and how animals develop and grow. - Animal nutritionists: Study the diets and digestive capabilities of animals. - Animal photographers and illustrators: Produce photos and drawings of animals for books, films etc. - Consultants: Advise others on animals and the environment. - Writers and producers: Inform others about animals and the environment through journalism, books and films. From http://www.zssa.co.za/index2.php?option=content&do_pdf=1&id=15
They effect animal populations because...... They do! if this ain't the answer you want, well then...... DEAL WITH IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!