Daniel Hunt Janzen (born January 18, 1939, in Milwaukee, Wisconsin[1]) is an American evolutionary ecologist and conservationist.

[1] His father, Daniel Hugo Janzen,[4] grew up in a Mennonite farming community and served as Director of the United States Fish and Wildlife Service.

Established in the 1990s, the ACG unifies several national parks, such as Santa Rosa, Guanacaste, Rincón de la Vieja, and Junquillal Bay, into a single administrative entity.

The ACG is recognized as a UNESCO World Heritage Site, highlighting its global ecological significance and Costa Rica's commitment to environmental conservation.

Their comprehensive strategy encompassed several key initiatives: Janzen's early work focused on the careful and meticulous documentation of species in Costa Rica, and in particular on ecological processes and the dynamics and evolution of animal-plant interactions.

[16][17] They employed the help of local Costa Ricans, converting their farming skills into parataxonomy, a term they coined in the late 1980s.

[26] These hypotheses have received varying degrees of support,[27] but are notable for having inspired a large and sustained body of research, as evidenced by the extremely high citation rates of many of his papers for decades after they are published.

In a 1977 paper 'Why fruits rot, seeds mould, and meat spoils',[30] Janzen proposed that microbes render food inedible (or at least distasteful) to vertebrates not just as a by product of microbe-microbe competition or accidental waste products, but as an evolutionary strategy to repel vertebrates consumers, who would otherwise eat the food resource and the microbes themselves.

[34] In 1985, realizing that widespread development in northwestern Costa Rica was rapidly decimating the forest in which they conducted their research, Janzen and Hallwachs expanded the focus of their work.

4% from world's plant, mammals, birds, reptiles, amphibians, fishes and insects diversity, all within an area less than 169,000 hectares (420,000 acres).

Not only must one fight against hundreds of years of ecological degradation, manifested in the form of altered drainage patterns, hard to eradicate pastures, compacted soils, exhausted seed banks, diminished adult and propagule stocks, proliferation of fire-resistant and unpalatable weeds from the old world tropics and sub-tropics.

"[18]: 134 Janzen has been subject to recognition many times in the US, as well as in Europe and Latin America; the monetary endowments of these prizes have been invested in the trust fund of the ACG or another of his conservation's projects in Costa Rica.