Janzen and his wifeWinifred Hallwachs have catalogued the biodiversity of Costa Rica. Through aDNA barcoding initiative, Janzen and geneticistPaul Hebert have registered over 500,000 specimens representing more than 45,000 species, which has led to the identification ofcryptic species of near-identical appearance that differ in terms of genetics and ecological niche. Janzen and Hallwachs developed some of the most influential hypotheses in ecology that continue to influence research more than 50 years later.[2][3]
In 1963, Janzen attended a two-month course in tropical biology taught in several field sites throughoutCosta Rica. This Advanced Science Seminar in Tropical Biology was the precursor to a Fundamentals in Tropical Biology course, which Janzen designed for theOrganization for Tropical Studies (OTS), a consortium of several North American and Costa Rican universities. Janzen went back in 1965 as an instructor and has lectured in at least one of the three yearly courses every year since.[6]
TheÁrea de Conservación de Guanacaste (ACG) is a prominent conservation area in northwestern Costa Rica, encompassing over 163,000 hectares of diverse ecosystems, including tropical dry forests, rainforests, and marine areas. 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. This integration aims to protect and restore the region's unique biodiversity and facilitate natural ecosystem regeneration. The ACG is recognized as a UNESCO World Heritage Site, highlighting its global ecological significance and Costa Rica's commitment to environmental conservation.[10]
Dr. Daniel Janzen, recognizing the necessity for a cohesive conservation strategy in Guanacaste, along with his wife, biologist Dr. Winnie Hallwachs, championed the establishment of a contiguous conservation area to facilitate natural ecosystem regeneration.
Their comprehensive strategy encompassed several key initiatives:
Restoring Tropical Dry Forests: Acquiring degraded pastures and enabling the recovery of natural vegetation.
Integrating Local Communities: Training local residents to serve as park guards, educators, and conservation advocates.
Fundraising for Land Purchases: Securing donations and forming partnerships with international organizations to purchase private lands and integrate them into the protected area.
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.[6]: 426 [11]In 1967, for example he described the phenological specialization of bee-pollinated species of Bignoniaceae,[12] amongst them a "kind of mass flowering", which Alwyn Howard Gentry in his classification of flowering named Type 4 or "big bang" strategy.[13] Janzen proposed many hypotheses that inspired decades of work by tropical and temperate ecologists (see below).
Miguel Altieri in his textbookAgroecology: The Science of Sustainable Agriculture says: "Janzen's 1973 article on tropical agroecosystems was the first widely read evaluation of why tropical agricultural systems might function differently from those of the temperate zones".[14][15]
In 1985, realizing that the area in which they worked was threatened, Janzen and Hallwachs expanded the focus of their work to include tropical forest restoration, expansion (through land purchases) and conservation.[16][17] They employed the help of local Costa Ricans, converting their farming skills intoparataxonomy, a term they coined in the late 1980s.[18][19] As of 2017, some 10,000 new species in theArea de Conservacion Guanacaste have been identified thanks to the efforts of parataxonomists.[19]
Janzen is known for proposing "characteristically imaginative and unorthodox" hypotheses.[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.[3]
One of Janzen's most famous ideas (from his most highly cited paper)[3] is now known as theJanzen-Connell hypothesis, as Janzen andJoseph Connell independently proposed the idea in 1970-1971. They both suggested that the high diversity of tropical trees was due, in part, to specialist enemies attacking seeds or seedlings that were particularly close to the parent tree or particularly densely clustered, thus preventing any one species from becoming dominant.[28]
Another influential idea[2] comes from Janzen's 1967 paper 'Why mountain passes are higher in the tropics'.[29] It proposes that tropical mountains are more of a barrier to species dispersal than temperate mountains because tropical species are less able to tolerate changes in temperature with elevation, having evolved and lived in relatively stable climates.
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. Evidence is mixed, and it is hard to test whether compounds evolved to deter other microbes or vertebrates,[31] but the idea has been widely incorporated into studies of vertebrate feeding from humans[32] to dinosaurs.[33]
Spondias mombin (Anacardiaceae) lost its megafauna seed dispersers in thePleistocene. Between fire in open pastures andseed predation bybruchid beetles in closed-canopy forest,S. mombin does not stand a chance. But, today, in Guanacaste, seeds are dispersed byWhite-tailed deer (Odocoileus virginianus) and some 15 other mammals, that feed mostly in forest edges, where bruchids are less likely to find the seeds and fires are not so frequent.[11]
Tropical dry forests are the world's most threatened forest ecosystems. In middle America there were 550 000 km2 of dry forests at the beginning of the 16th century; today, less than 0.08% (440 km2 ) remains.[34] They have been cleared, burnt and replaced by pastures for cattle raising,[35] at an ever-faster rate during the last 500 years.[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. Janzen and his wife helped to establish theArea de Conservación Guanacaste World Heritage Site (ACG), one of the oldest, largest and most successfulhabitat restoration projects in the world. They began with theParque Nacional Santa Rosa, which included 100 km2 (25,000 acres) of pasture and relictual neotropical dry forest and 230 km2 (57,000 acres) of marine habitat.[16] This eventually became theÁrea de Conservación Guanacaste, located just south of the Costa Rica-Nicaragua border, between the Pacific Ocean and theCordillera de Tilaran which integrated four different national parks. Together these house at least 15 differentbiotopes, viz (mangroves, dry forest and shrubs, ephemeral, rainy season, and permanent streams,fresh water andlittoral swamps,evergreen rain- andcloud forests...) and ca. 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).[36] It is one of the oldest, largest and most successfulhabitat restoration projects in the world. As of 2019, it consists of 169,000 hectares (420,000 acres).[36] The park exemplifies their beliefs about how a park should be run. It is known as a center of biological research,forest restoration andcommunity outreach.[20]
Habitat restoration is not a simple matter. 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 andpropagule stocks, proliferation of fire-resistant and unpalatable weeds from the old world tropics and sub-tropics.[37] Also one is faced with the difficulties of changing a culture which coevolved with, profited from and can become miserable with such a system.[38][39][40]
For this reason ACG was conceived as a cultural restoration project, which, to paraphrase its natural counterpart, ought to be grown as well. ACG integrates complementary processes of experimentation,habitat restoration and cultural development.[18]: 89–91 [41]The techniques used include:
Active restoration, artificial dispersal of propagules from plant species native to the Guanacaste habitats[41]: 57, 73
Passive restoration by means of fire, anti-poaching and herbivore control[41]: 33, 73
Janzen is married to ecologistWinifred Hallwachs, who is also his frequent research partner. Of Hallwachs, Janzen has said, "We did these things together,"[18]: 132–136 and "we are very much together in perceiving things the same things....Since I'm the vocal member, it's then attributed to me. But I would say these ideas and directions and thoughts and actions are easily fifty-fifty attributable."[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. Prizes and distinctions garnered by Janzen include:
2002, Honorary Fellow of the Association for Tropical Biology (and Conservation) (ATBC)[57]
2006, Winner, National Outdoor Book Awards (NOBA), for100 Caterpillars: Portraits from the Tropical Forests of Costa Rica (2006), Design & Artistic Merit Category.[58]
2011,BBVA Foundation Frontiers of Knowledge Award of Ecology and Conservation Biology for his pioneering work in tropical ecology and his contributions to the conservation of endangered tropical ecosystems throughout the world, drawing on an understanding of plant-animal interactions. Janzen acknowledged the role of his wife and long-term research partner, ecologist Winnie Hallwachs, to the work being recognized.[59][60]
2013,Wege Foundation $5 million grant to the Guanacaste Dry Forest Conservation Fund (GDFCF), founded in 1997 by Dan Janzen and Winnie Hallwachs.[61]
The following is a selection of Janzen's publications that are not otherwise listed.
Rosenthal, Gerald A.; Janzen, Daniel H., eds. (1979),Herbivores: Their Interaction with Secondary Plant Metabolites, New York: Academic Press, p. 41,ISBN0-12-597180-X
Janzen, Daniel H. (September 1966). "Coevolution of Mutualism Between Ants and Acacias in Central America".Evolution.20 (3):249–275.doi:10.2307/2406628.JSTOR2406628.PMID28562970.
Janzen, D. H. (1986).Guanacaste National Park : tropical ecological and cultural restoration. San José, Costa Rica: Editorial Universidad Estatal a Distancia.ISBN9977-64-316-4.
^Burgos, Ana; Maass, J.Manuel (December 2004). "Vegetation change associated with land-use in tropical dry forest areas of Western Mexico".Agriculture, Ecosystems & Environment.104 (3):475–481.doi:10.1016/j.agee.2004.01.038.
^"The Four Awards Bestowed by The Academy of Natural Sciences and Their Recipients".Proceedings of the Academy of Natural Sciences of Philadelphia.156 (1). The Academy of Natural Sciences of Philadelphia:403–404. June 2007.doi:10.1635/0097-3157(2007)156[403:TFABBT]2.0.CO;2.S2CID198160356.
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“Costa Rica : Paradise Reclaimed”, Profile of Dan Janzen inNature,MacArthur Foundation (WNET Television station : New York, N.Y., 1987)
