Samantha

=Pollination of the Columnar cacti //Weberbauerocereus weberbaueri//=



= **Introduction** =

Biotic pollination is one of the many forms of pollination that serve as a key factor to the sustainability of plant species. The importance of this type of pollination is seen in a cactus species located in the desert of Arequipa, Peru. Cacti have developed adaptations to their arid habitats, and are able to withstand times of drought. Although they are able to perform asexual reproduction, the rates of pollination are much higher if helped out by other species. For the //Weberbauerocereus weberbaueri// columnar cactus, there are three species that help to pollinate its flowers. The primary species involved with this interaction include the Peruvian long-nosed bat (//Platalina genovensium)//, the Giant Hummingbird (//Patagona gigas//), and the Oasis Hummingbird (//Rhodopis vesper//). They helped to conserve the population of this plant throughout the year, and are increasingly helpful during drought. This symbiotic interaction helps to maintain a healthy ecosystem in this remote area of the world.

= **Organisms involved** =

//Weberbauerocereus weberbaueri// is a columnar cactus from the Family Cetacaea. It is part of the Tribe Trichocereeae, which is primarily found in South America. This particular species is located in Arequipa, Peru at the foothills of the Andes Mountains. It lives in a desert environment, and is the keystone species of the area. Many organisms are dependent on the pollination of these cactus and the fruit that it produces. The flowers produced are a tubular shape. They range in colors and open at systematic times of the day and night. This method makes the cactus plant particularly favorable since it plays to the attributes of the species, which it is pollinated by. The flowers open in the late afternoon and remain open throughout the night until late morning, when they close. The cactus plant has the ability to withstand the desert environment due to their simple qualities and structures. They have developed roots that are close to the soil surface, allowing them to pick up any water that may be deposited. They reserve this water for times of severe stress such as drought. In addition, they have pores on the outer surface, which has a waxy coating to help keep in more water. These pores remain closed throughout the day and only open at night to allow for some moisture to seep through. Their prickly spines are not only a defense mechanisms, but allow them to photosynthesize as well. What may look like a primitive structure is actually highly advanced, and enables them to withstand the changing environment of the arid desert.

//Platalina genovensium// is the Peruvian Long-nosed bat. It is classified as a near threatened species and therefore is not very abundant. Only about seven colonies in Arequipa have been recorded, totaling in at about < 100 bats (Sahley, 1996). The bats are nocturnal, tending to visit the cacti flowers at night, feeding on the nectar provided. They are the only bat species that pollinates and disperses the seeds of the columnar cacti along the Andes. They are very specific to a narrow range of habitats that requires this symbiotic relationship with the columnar cacti. They prefer flowers that are white and funnel formed with a pungent smell and large amounts of nectar and pollen. Not is actually known about this species, and more research is being conducted.

//Patagona gigas// is the giant hummingbird, located in Peru, Chile and Ecuador. It is mainly found in higher altitudes and is the largest of the hummingbird family measuring at about 21 cm. //Rhodopis vesper// is the Oasis Hummingbird, distributed in west Andes of Peru and Northern Chili. Both species prefer tubular flowers with red coloring, are odorless and diurnal, and produce copious amounts of nectar and pollen

//Patagona gigas// //Rhodopis vesper// = **Biological Interaction** =

This is a classic demonstration of mutualism. The cactus allows its flowers to open at night, when the bats visit, and to remain open throughout the late morning, when the hummingbirds visit. They close up again until late afternoon when the hummingbirds feel the need to make a food stop once again. Then the cycle continues. The pollination that is preformed by these species has increased the amount of flowers that grow fruits, which typically take two months to develop after pollination. Studies preformed by Sahley, have shown the bats to be the primary pollinating species. This is why the livelihood of these bats is so important, because without them, a whole ecosystem could potentially dissolve. This cactus species produces fleshy fruit and nectar year-round, making it a prominent and reliable food source. Not only does this symbiotic relationship benefit their species, but it also benefits all other organisms that live in the area. Many rely on the fruits of the these cacti, and without this relationship, the amount of fruit produced would drastically decrease.

= **Impact/Importance** =

The Peruvian long-nosed bat and the hummingbird species help sustain the keystone species of Arequipa desert, //W. weberbaueri//. A study preformed by Sahley showed 70% of flowers pollinated by bats developed fruits, 55% of flowers pollinated by hummingbirds developed into fruits and self-pollination contributed up to 40%. As a result, the Peruvian long-nosed bat is the primary pollinator of the cactus plant. To show how heavily these species rely on each other, Sahley had preformed her experiment before, during and after the el Niño (1992-1993). The event caused long-term drought and therefore major stresses not only on the cacti, but also on the bat species as well. During this time, results showed lower pollination by bats, however there was no change in the hummingbird species. After the drought, the bats did not seem to repopulate very quickly. There questions as to why varied, but never reached a conclusion.

=Current Research=

Overall, there has been limited research conducted in the more recent years. The main advocate for performing these studies was Sahley who has moved on to other studies around Peru and Central America. As a result it leaves us with many questions: Where did the bats go? Will this species of cacti decline due to decrease in bat pollination? And will the bat population ever repopulate Arequipa? These are questions that have been asked and most likely are being studied today, however results remain inconclusive. =References=

=
 Sahley, C., 1996. “Bat and Hummingbird Pollination of an Autotetraploid Columnar Cactus, // Weberbauerocereus weberbaueri (Cacataceae).” American Journal of Botany. // 83(10):1329-1336.  ======

=
 Sahley, C., 1995. “High in the Andes Mountains, the Peruvian long-nosed bat helps sustain a critical food supply for a fragile ecosystem.” // Bats Magazine. 13(3) // ======

Page authored by Samantha Bates, student of Dr. Michelle Lum at Loyola Marymount University, Los Angeles.