Historically, zoos have focused on the exhibition and maintenance of "diurnal, social, large, colorful, cute, typically mammalian and usually African species" . Today, ex situ zoo-based breeding programs are still biased toward the so-called "charismatic megavertebrates." This has recently found justification in designating large mammals as "flagship" or "keystone" species. The strong impact of these species on visitors, in turn, permits zoos to remain viable as institutions through increasing public awareness of wildlife and by funding their in situ conservation activities .
The traditional emphasis on megafauna has at least two shortcomings. People receive a very narrow view of the animal world, as being dominated by large creatures, and continue therefore to ignore a major portion of the planet's biodiversity and, conversely, the problems of just knowing and preserving it. Additionally, important regions or areas of global biodiversity are almost totally overlooked in zoo plans if those regions lack large animals. Thus, we see flourishing in every zoo multi-million dollar African savannahs and Asiatic jungles, but less commonly find installations focusing on the Atlantic Forest of Brazil (although lion tamarins of the genus Leontopithecus represent one of the most successful zoo conservation stories), on the Colombian Chocò, the Philippines or the Eastern Arc Forests of Tanzania, all identified as among the biologically richest and unique regions on the planet .
Also, the loss of biodiversity on islands is not adequately emphasized in current zoo exhibition plans, although some island species are currently the focus of zoo-based captive breeding programs.
The decline of many large mammals is often perceived as caused by direct human activities such as hunting for food, trophies, skins, and other body parts, i.e., problems relatively easy to denounce and occasionally resolve. These proximate causes may hide the principal reasons for loss of biodiversity such as human population growth, habitat alteration, and introduction of alien organisms-threats to which smaller vertebrates, invertebrates, and plants may be the most susceptible.