Monday, April 19th, 2010 | Author:  | 32,391 views - starting Aug 9/09

 

Leptonycteris curasoae. Copyright US Fish & Wildlife Service.

Recently, the explosion of agave nectar consumption has dramatically increased demand for the agricultural production of agave crops.  Agave nectar is advertised as a safe and nutritious alternative sweetener that can be enjoyed by everyone, especially diabetics, without the potential side-effects suffered from consuming sugar cane, honey, corn syrup, and sugar alcohols.  However, agave agriculture is not an ecologically sustainable practice.  The biodiversity of agave plants, their native desert ecosystems, and the pollinator bat species that depend on agave for food are all at risk.

It has become widespread knowledge that the world’s pollinators are dwindling.  Thanks to the global voices of entomologists (scientists who study insects) and ornithologists (scientists who study birds), public concerns about the precipitous decline in pollinator populations have motivated successful conservation strategies to help protect commonly loved species such as honey bees, Monarch butterflies, and various hummingbirds.

However, the number of plant pollinators whose existence is under threat is, sadly, far greater than what most people realize.  One very important group of pollinators, bats, is often overlooked; yet, in many ecosystems bats are primary pollinators and dispersers of seeds for thousands of plants, including plants used and consumed by humans.

Agaves are among the plants that some species of bats pollinate. However, what makes this relationship especially unique is that bats and agaves are reliant upon each other—loss of one will effect dire consequences for the other. So how does the agave nectar industry affect the ecology of bats and of agave? Let’s take a closer look at the biology of agaves and bats in South America.

 

The Life of Agaves

Agave plants are botanically classified as lilies and their shallow roots and succulent leaves make them exceptionally well-adapted to desert ecosystems.  There are more than 250 documented species, which range in height from ground dwelling rosettes to species with leaves extending up to 2 metres.  All are native to arid ecosystems of southwestern U.S., Caribbean islands, Central America, and tropical South America.  They are also grown ornamentally around the world.  The name agave, derived from the Greek word agaue, means “noble”.

Most species are long-lived, attaining ages of 10—25 years.  In general, they reach sexual maturity at about 8—25 years (maturity varies with species, availability of nutrients and other environmental resources, geography, etc.).  Agaves can reproduce sexually or asexually.  Sexual reproduction involves growth of a single, tall flowering stalk (reaching 2—12 metres, depending on the species) studded with multiple large flowers.  The flowers open at or after dusk, and close at or before dawn; hence, they are most receptive to nocturnal and crepuscular pollinators.  The flowers die after 4—7 days.

If the flowers have been pollinated, then a fruit develops, dries up when it is ripe, and breaks open to disperse the seeds to the wind.  The parent plant quickly dies after the release of the seeds.  In this way, sexual reproduction preserves the genetic diversity of the species because pollen is distributed between unrelated plants by bats that visit the flowers for nectar.

If the flowers are not pollinated during their short life span, then no fruit (and therefore no seeds) develop.  The parent plant reproduces asexually (by forming buds—called bulbils—from the flowering stalk or budding off from the roots) wherein each offspring is genetically identical to the original plant.

 

Farming Agaves

Farmed agaves never reach sexual maturity because the harvesting methods preclude the growth of flowering stalks.  Agave crop plants are therefore not available to bats for food.

Agave crop plants are allowed to grow to the onset of sexual maturity or are selected in the wild when the flowering stalk is almost mature.  Before the flowering spike matures, farmers slice it off.  The remaining base of the plant swells as nutrients accumulate in the primary stem.  When the upper plant begins to die (for example, leaves begin to brown and the primary stem begins to shrink back), it is severed from the roots and the leaves are removed from the stem.  These “agave heads” or “piñas” are ground to a pulp in a factory, and the agave-based sweetener is produced in a multi-step process.

First, the milled pulp mass is centrifuged to fractionate a polyfructose liquid (a complex sugar made up of many individual fructose molecules), which is then extracted and heated to make a concentrate.  Further steps of centrifugation, filtration, and heat purify the concentrate and remove particulate matter.  The polyfructose extract is then treated with charcoal and cationic (positive charge) plus anionic (negative charge) resins to demineralize it.  It is then subjected to heat-induced or enzyme-controlled hydrolysis (break down) to produce a refined polyfructose extract.  Once diluted, this final product is sold as a sweetener.

Some commercial processes involve black mould (Aspergillus niger) enzyme hydrolysis to produce the final sweetener, which may render the product unsuitable for people sensitive to yeasts, moulds, and fungi.  The high fructose and inulin (fructo-oligosaccharides also known as FOS) content may be unsuitable for people with IBS or IBD, fructose malabsorption, liver cirrhosis, hepatitis, or fatty / congested liver (also known as liver steatosis).  Some products, labelled “agave syrup”, may consist of agave nectar mixed with other sweeteners (including the highly processed ‘high fructose corn syrup’), a combination which also may be unsuitable for some sensitive people.

Agave ‘nectar’ is technically not nectar at all because it is not produced by the flower proper.  The relatively inexpensive syrup that is sold almost ubiquitously in North America today is not even the delectable agave sap, termed “aguamiel” (literally, honey water), which is the nourishing secretion that collects within a small receptacle inside the base of the flowering stalk as the flowers mature.  The agave ‘nectar’ that is being sold commercially is simply a refined syrup obtained from processing the starch- and sugar-rich tissues of the agave plant stalk.

 

Unsustainable Agave Agriculture

Intensive agave farming is problematic for three main reasons.  First, agricultural cultivation of agave crops is not ecologically or economically sustainable.  Second, harvesting of wild agave plants is not ecologically sustainable.  Third, the mutually dependent relationship with endangered bat pollinator species is negatively impacted by the agave commercial trade.

Why is agricultural cultivation of agaves not ecologically sustainable?  Most importantly, any conversion of native ecosystems into other forms of land use, including agriculture, reduces the agave food supply for bats and other animals.

Typical of monocultures that intrinsically perpetuate loss of biodiversity, farmed agaves suffer decreased individual plant health, increased susceptibility to insect infestations and pathogenic infection, and reduced resilience to variation in the environment (including soil composition) and climate.

To prevent crop death weakened plants are sprayed with synthetic pesticides, which not only contaminate the crop but also poison the ecosystem and groundwater.  Some examples of pesticides that may be used on agaves include 2, 4-D (all forms), atrazine, clopyralid, dicamba (all forms), dichloprop (2,4-DP), hexazinone, MCPA (all forms), paraquat, picloram (all forms), and tebuthiuron.

Organically grown and wild-harvested agaves are free of these chemicals.  However, there are relatively few truly organic agave farms and wild harvesting decreases genetic diversity because it results in loss of adult plants or it increases the frequency of asexual reproduction.  (Asexual reproduction also decreases genetic diversity and therefore makes plants more susceptible to pest infestation and drastic changes in climate or environment and resources.)

Wild agave populations are already under threat due to habitat loss and other anthropogenic pressures (including harvesting for production of agave nectar and mezcal, also known as tequila).  Agave desert ecosystems are intrinsically fragile, vulnerable, and incapable of adapting rapidly enough to survive incessant disturbance and habitat development.

 

How Bats Come Into the Picture

Bats are incredibly fascinating animals.  Fortunately, scientists and the general public are starting to appreciate the integral role bats play within global ecosystems.  Unfortunately, however, it is also becoming alarmingly apparent that most bat populations are quite sensitive to loss of habitat, loss of high quality food sources, disturbance during critical periods such as parturition and hibernation, environmental pollution, mining, and disease.  With more than 1,150 extant bat species worldwide, a shocking 474 species are currently endangered or near threatened.

Bats consume tonnes (literally!) of insects each night, pollinate and disperse the seeds of various plants, facilitate forest regeneration, and provide an abundant supply of plant-fertilizing guano.  In some cases, bats have co-evolved closely with the plants they pollinate.

Leptonycteris curasoae, the Lesser Long-tonged bat. Copyright M. Tuttle.

Chiropterologists (scientists who study bats) have observed that the morphology of some bats’ heads (particularly the snout, tongue, and neck) creates a perfect fit with the shape, depth, and size of the flowers they pollinate.  The flower, in turn, is most effectively pollinated by a particular bat species and it adapts to maximize pollinator visitation.

For example, flowers of large agaves grow on tall stalks, open only at night, produce scents attractive to bats, and bloom most abundantly during the time of year when bats are present.  Most large, long-lived and commercially exploited agave species are dependent on bat pollination for sexual reproduction, population persistence, maintenance of genetic diversity, and geographic dispersion.

Some moths, birds, and bees also pollinate large agaves, but bats seem to be much more effective at this task.  In the absence of bat pollination, plant reproductive output can be greatly compromised (for example, there is decreased seed production—up to a 3,000-fold reduction in seed set, decreased distance of pollen dispersion, decreased number of pollinated plants, and increased incidence of asexual reproduction).

The mutually dependent relationship between agaves and bat pollinators is compromised by the agave commercial trade.

Four species of bat are the primary pollinators of large agaves: Curaçaoan Long-Nosed bat (Leptonycteris curasoae), Mexican or Greater Long-Nosed bat (Leptonycteris nivalis), Lesser Long-Nosed bat (Leptonycteris yerbabuenae), and Mexican Long-Tongued bat (Choeronycteris mexicana).

All four of these species are Threatened or Endangered.  They are listed internationally by the IUCN (International Union for Conservation of Nature and Natural Resources) and nationally by the U.S. Fish and Wildlife Service.

Agaves are primary food sources for all 4 bat species, and large areas of abundant flowering agaves are necessary for providing sufficient energy and nutrient intake for the bats.  Agave food sources are especially critical during migration (late fall and early spring) and for pregnant and lactating females (May to July).

Populations of these bat species are steadily declining due to loss of foraging and roosting habitat.  Harvesting wild and domestic agaves negatively impacts populations of all 4 bat species.

Due to the threat this agricultural practice poses to populations of bats and other animal pollinators, agave nectar is a ‘vegan-unfriendly’ product.

 

Implications for Agave Farmers

While it is easy for North American consumers to focus on ecological principles, nutritional concerns, or aesthetic issues when making product choices, the reality is that some people — in fact, some communities — may depend on the income generated by agave farming.  However, socioeconomic analyses of major agave farm communities suggest that the industry does not provide a suitable livelihood for most agave farmers.

One study showed that overall, agave farmers may not benefit from superior crop yield or income by growing agaves in lieu of other commercial crops.  In this study, the socioeconomic state of major agave-producing regions in Mexico did not appear to be significantly improved by the harvesting of agaves compared to the production of other commercial crops or the development of other industries.

Another study exposed an even worse scenario for Mexican farmers.  In Mexico, the agave industry is apparently controlled by major tequila companies, namely Cuervo, Sauza, Herradura, and Cazadores, that either buy out agave farmers in various communities or control the market such that individual farmers can no longer afford to maintain an independent agave farm.

When tequila companies purchase an independent, family-owned farm, several things change: the farmer is bound to the contract with the tequila company and is obligated to sell his or her agave for whatever price is set by the company (farmers lose autonomy and any leverage for influencing the market); agricultural practices become less traditional, more mechanized, more dependent on chemical inputs, and less environmentally friendly or sustainable; and farmers’ incomes decrease overall and become less predictable.

The agave syrup industry was created by tequila companies that intended to stabilize market demand for agave. However, the environmental and humanitarian repercussions of this new industry are serious drawbacks.

On the other hand, there are caveats to all forms of habitat development and an alternative to agave crop production may bring about other unforeseen ecological damage.

One of the purported benefits of agave farming is that it allows exploitation of dry, sandy soils that are generally unsuitable for cultivation of other commercial crops.  This is a controversial point as agricultural enterprises in hostile environments generally result in increased soil erosion, mineral-depleted and nutrient-impoverished soils, and poor long-term sustainability of farms.

 

The Most Important Thing to Remember: Truly Appreciate the Agave’s Sweet Gift

While it is not reasonable to assume that the commercial sale of agave nectar will, or should be, completely stopped, it is important to respect, and be mindful of, where our food comes from.  Increasingly, consumers are becoming informed about the sources of their products, and are becoming responsible shoppers.  It is time to take our conscientious habits one step further.

Think about more than just “food kilometers” the next time you consider purchasing agave nectar or food products containing this as an ingredient.  This product should be regarded as a luxury to be consumed in moderation.

Plants and animals have nourished humans for millennia.  It is our responsibility, as consumers and as important members of natural ecosystems, to avoid excess consumerism in every area of our lives.

 

References

Arita, H.T., and D.E. Wilson. 1987. Long-Nosed Bats and Agaves: The Tequila Connection. BATS Magazine. Bat Conservation International. 5(4): 3—5.

Arizaga, S., E. Ezcurra, E. Peters, F.R. de Arellano, and E. Vega. 2000. Pollination ecology of Agave macroacantha (Agavaceae) in a Mexican tropical desert. II. The role of pollinators. American Journal of Botany. 87(7): 1011—1017.

Bowen, S., and A. Valenzuela Zapata. 2009. Geographical indications, terroir, and socioeconomic and ecological sustainability: the case of tequila. Journal of Rural Studies. 25(1): 108—119.

Burwell, T. 1995. Bootlegging on a desert mountain: The political ecology of Agave (Agave spp.) demographic change in the Sonora River Valley, Sonora, Mexico.  Human Ecology.  23(3): 407—432.

Dalton, R. 2005. Saving the agave. Nature. 438: 1070—1071.

IUCN (International Union for Conservation of Nature and Natural Resources). 2008. IUCN Red List of Threatened Species. www.iucnredlist.org/

Martínez-Salvador, M., L. Beltrán-Morales, R. Valdez-Capeda, H.R. Arias, E. Troyo-Dieguez, B. Murillo-Amador, J.J. Galindo, and A. Ortega-Rubio. 2007. Assessment of sustainability performance on the utilization of Agave (Agave salmiana ssp crassispina) in Zacatecas, Mexico. International Journal of Sustainable Development and World Ecology. 14(4): 362—370.

Medellin, R.A. Pers. comm. Instituto de Ecología, Universidad Nacional Autónoma de México. medellin@miranda.ecologia.unam.mx

Molina-Freaner, F. and L.E. Equiarte. 2003. The pollination biology of two paniculate agaves (Agaveaceae) from northwestern Mexico: contrasting roles of bats as pollinators.  American Journal of Botany.  90(7): 1016—1027.

NatureServe. 2009. NatureServe Explorer.  www.natureserve.org/explorer

Patent Storm. 1998. US Patent 5846333. Method of producing fructose syrup from agave plants.

Scott, P.E.  2004.  Timing of Agave palmeri flowering and nectar-feeding bat visitation in the Peloncillos and Chiricahua Mountains.  The Southwestern Naturalist.  49(4): 425—434.

Slauson, L.A.  2000. Pollination biology of two chiropterophilous agaves in Arizona.  American Journal of Botany.  87(6): 825—836.

U.S. Environmental Protection Agency.  2008.  Pesticides: Endangered Species Protection Program. Maricopa Country, AZ. Arizona Agave.

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12 Responses

  1. 1
    Cindy 

    I appreciate your comprehensive article about Agave farming.

  2. 2
    Alicia Fritz 

    This is a well done article that I have bookmarked for future reference.

  3. 3
    Meg 

    Do you have any idea how much nectar one bat consumes in a day/night. The lesser long nosed bats come to my hummingbird feeders this time of year and I am trying to figure out how many I have. They are consuming 10 cups of sugar water before the feeders are drained. Post here http://mostlyphotos.wordpress.com/2011/09/01/bat-night-2011/

  4. 4
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    Awesome site you have here!

  6. 6
    Ismail Afik Hakim 

    Very nice and helpful information about this topic. I like the way you explain things. Keep working. Thanks.

  7. 7
    rebecca suffield 

    This really answered my questions, thank you!

  8. 8
    Kaye 

    I had no idea! Thanks for this!

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  1. what’s wrong with agave syrup? “… The harvested product goes through about as many transormative stages as High Fructose Corn Syrup to become Agave Nectar. Most of the pesticide residue is shed somewhere between the first fractionating and the last hydrolysis of the pulp mass. But the people who live around the agave fields and work in them aren’t as isolated from pesticide exposure as the developed world consumers are. Is it neighborly to visit the Fifth Horseman of Agribusiness upon our hapless economic dependents? Let alone the disappearing long-nosed bat species of the Jalisco region? …”

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