Why Is The Saguaro Cactus A Keystone Species

Charles McDonald

The saguaro (pronounced suh-WAR-oh) cactus, along with the roadrunner, chili pepper, and howling coyote, has become one of the iconic representations of the desert Southwest. It has been depicted inexplicably in places where it could never actually exist in works of art, movies, and advertising.

Actually, saguaros are only found in a tiny area of California, Mexico, and Arizona’s Sonoran Desert. For strong root anchorage, they require rocky soils, more rainfall than is typical in low deserts, and mild temperatures without any extended freezing. On the bajadas that make up the lower slopes of desert mountain ranges, these circumstances are present. National forests include some of the best saguaro habitat. To the north and east of Phoenix, in the Tonto National Forest’s New River, Mazatzal, and Superstition mountains, are magnificent stands of these enormous cactus. Similar spectacular stands can be seen in the Santa Catalina Mountains on the Coronado National Forest, which is located north of Tucson.

The average saguaro is large and ancient. Before they bloom for the first time, plants are at least 50 years old, and the first side branches often appear when they are 75 years old. Plants have a 200-year lifespan. Nearly 50 feet tall and 10 feet around, a huge saguaro can be quite large. They stand taller than any other plants in the surrounding desert scrub. Water-filled big plants can weigh up to 6 tons.

Many desert creatures rely on the saguaro as a keystone species for food and refuge. From late April to early June, hundreds of flowers on saguaros bloom multiple times daily. The blooms begin to bloom at night and end the next afternoon. Lesser long-nosed bats spend the nighttime among the flowers. The following morning, insects, primarily honey bees, and birds, primarily white-winged doves, visit the blooms. In early July and June, the fruits reach maturity. The rich crimson pulp, which is studded with up to 2,000 small seeds, is revealed when the skin splits into three or four quarters and begins to peel back. The fruits are about the sole moist food source for many birds, animals, and insects during this time of year, when the drought is at its worst, in early July.

Many birds find saguaros to be great nesting sites. Both gilded flickers and gila woodpeckers dig nest holes in the fleshy stalks. In order to provide other species like elf owls, house finches, ash-throated flycatchers, and purple martins a chance to occupy former woodpecker nests, the woodpeckers typically dig new nest holes every year. In the angles formed by the main stems and the arms, red-tailed hawks and other large birds build their nests. Many birds find that tall saguaros provide suitable perches for resting and hunting.


The Carnegiea gigantea saguaro cactus, which typically grows to a height of 40 feet, is the biggest cactus in the United States. The saguaro plays a crucial role in the Tohono O’odham people’s culture and offers food and shelter to a range of desert creatures. According to some reports, the saguaro can be ecologically related to almost every other species in its habitat, including people.


Only in the Sonoran Desert of the United States and Mexico does the saguaro cactus flourish. Altitude and below-freezing temperatures restrict its range.

The saguaro’s body and arm-like branches have firm spines and bristles, and they are pleated and ridged. White flowers emerge in May and June, followed by bright-red fruits that may each contain as many as 2,000 tiny black seeds. Saguaros can weigh more than 6 tons because they are primarily made of water (759 percent of the plant’s bulk).

Animals and people both place a great value on saguaro cacti. Large birds construct stick nests among the saguaro’s arms, while little birds excavate nest chambers inside its pulpy flesh. Birds, bats, animals, reptiles, and insects can all benefit from the nectar, moisture, and nourishment that saguaro blooms, fruit, and flesh supply. The Hohokam people of the present-day Tucson region employed saguaros in their daily lives, according to archeological findings. The saguaro is a sacred plant that is used in ceremonies and as food by the contemporary Tohono O’odham, who are thought to be the Hohokam’s successors.

Saguaros grow slowly. A saguaro grows between 1 and 1.5 inches in the first eight years of its existence in Saguaro National Park; branches often start to sprout after 50 to 70 years of age. It could take up to 100 years for the branches to develop in drier regions. Saguaros attain adulthood at around 125 years of age and start to produce flowers around the age of 35. A saguaro’s lifespan is roughly 150–175 years on average, but certain species can live for 200 years or longer.

Status and Threats

The saguaro is a typical Sonoran Desert plant and is not a threatened species. The introduction of alien plants and habitat loss are the two major challenges to its current state that are caused by humans. Because they can both outcompete the saguaro and raise the risk of fire in a setting not suited to them, exotic plants, in particular buffelgrass, fountain grass, and red brome, are hazardous. Therefore, it is essential to regulate fire and exotic plants in Saguaro NP in order to keep a healthy saguaro population. Theft, attempted transplants, and vandalism are some additional dangers to saguaros.

Cacti are they a keystone species?

Robert Paine, a prominent environmentalist, altered a section of the Washington State shoreline in the 1960s and achieved a significant environmental accomplishment. He removed every starfish species in one area in Makaw Bay in an effort to comprehend the food chain in a tidal ecology. He came to understand that some species play disproportionately large roles in the overall structure and function of their environment as a result of how quickly the entire ecosystem changed. Others have the power to upend an entire community of plants and animals with their disappearance, while some creatures have little impact on the ecosystem in which they live. These important organisms have a name thanks to Paine: keystone species. Here is a closer look at keystone species found all around the world and at various points in the food chain.

What Is a Keystone Species?

A keystone species, which can be any type of creature, including bacteria, fungus, and even animals and plants, is what binds a habitat together. Even though it might not be the biggest or most numerous species in an ecological community, the removal of a keystone triggers a series of events that drastically alter the habitat’s structure and richness. These are the living entities that play a crucial role in how their ecosystem functions, despite the fact that all of an ecosystem’s numerous components are intimately linked.


Keystone predators, such as wolves and sea otters, have an effect on other predators as well as other animal and plant species farther down the food chain by controlling the populations and distribution of their prey. When a keystone predator is gone, the population of the prey it once hunted might expand, driving out other creatures and lowering the diversity of species. A trophic cascade is the name given to this chain reaction.


The ecosystem depends heavily on keystone prey, which can range from Antarctic krill to Canadian snowshoe hares. They are an essential source of food for predator populations, and unlike certain other types of prey species that are more prone to going extinct or becoming scarce within an ecosystem, they are hardy animals.

Ecosystem engineer

Beavers, African savanna elephants, and other ecosystem engineers build, alter, or maintain the environment around them instead of affecting the food source. They affect the presence and behavior of other creatures and contribute to the habitat’s overall biodiversity.


Keystone mutualists are two or more organisms that interact in ways that are mutually beneficial to both. When one species is disrupted, it affects the other and, eventually, the ecosystem as a whole. These partnerships frequently consist of pollinators, such as hummingbirds, who depend on particular plants for their survival and those plants’ ability to reproduce.

What Effect Do Keystones Have on an Ecosystem?

Keystone species influence the variety and abundance of other species in a habitat, helping to preserve the local biodiversity of an ecosystem. They almost always play a key role in the local food chain. The fact that a keystone species performs a crucial ecological function that no other species can is one of its defining traits. An entire ecosystem would drastically shift or vanish altogether without its keystone species. It’s crucial to remember that a species’ function might vary from one ecosystem to the next, and a species that is valued as a keystone in one place might not be in another.


Robert Paine’s idea of keystone species was first introduced by the sea star, Pisaster ochraceus, a keystone predator found in the tidal pools of northwest North America. When contrasting two areas of shoreline—one from which he physically removed the sea stars and threw them out to sea—Paine found that the starfish—despite being relatively uncommon—had a significant impact on biodiversity on the terrain where they remained. Mussels quickly displaced several of the 15 original species, including algae, limpets, anemones, and sponges, on tidal outcrops devoid of the predatory sea star. The biodiversity of Paine’s ecology, devoid of starfish, decreased by over half in just one year.

Sea otters

Sea otters, which are native to the northern Pacific Ocean, are essential to the survival of coastal kelp forests. Kelp forests, which are dense communities of brown algae that rise above the ocean floor, offer a variety of fish, marine mammals, and other species with food, shelter, nascent habitat, and hunting grounds. However, they are susceptible to predation by marine invertebrates.

In particular, sea urchins graze on kelp and become bigger and more numerous when there are no predators like sea otters to keep them in control. Sea urchin “herds” as large as 30 feet long have been observed to consume kelp at a rate of up to 30 feet per month while leaving a desolate sea floor in their wake. Fortunately, sea otters have a voracious appetite and can eat up to 25% of their body weight each day. Because of their voracious hunger for these spiky marine creatures, otters are able to manage sea urchin numbers and maintain healthy kelp forests.


Beavers are ecosystem architects who significantly alter their physical surroundings. The dams they build flood the surrounding area, creating ponds and marshy meadows that provide as habitat for a variety of animals and plants. Wetlands serve as a refuge, a nursery habitat, a breeding and feeding ground for freshwater fish, insects, amphibians, birds, other creatures, and plants, including those that are threatened and endangered. In addition to enhancing stream water quality, beaver dams and the wetlands they create also replenish undersea aquifers, ease drought and water shortages, lessen floods, store nutrients for plants, and decrease stream erosion.


A top predator that has an impact on the environment as a whole are gray wolves. According to studies, wolves help preserve healthy stands of trees in the landscape by keeping elk populations in check by preventing them from over-browsing on willow and aspen. Wolf populations benefit from their uneaten meal scraps, which increase the food supply for scavengers like eagles, coyotes, and bears.

Only a small portion of the gray wolf’s historic range exists in the lower 48 states, and it is still an endangered keystone species. Despite this, the Trump administration is working to repeal wolf protections put in place by the Endangered Species Act in 1974, putting the animal’s recovery in jeopardy.


The African savanna elephant, a keystone species in eastern and southern Africa, eats up to 300 pounds of grass every day. They are ecosystem engineers that protect bright, open regions where grasses can thrive by removing and consuming enormous amounts of small trees and shrubs that would otherwise turn into forest or scrubland. Other herbivores like antelopes, wildebeests, and zebras are supported by this flora, which also offers warm, dry soil for smaller animals like mice and shrews to burrow into. These prey animals then provide food for carnivores like lions, hyenas, and cheetahs. Elephants also disperse plant seeds to new locations through their excrement. In fact, certain plants have developed to the point where they may now germinate more readily after being digested by an elephant. Poachers and trophy hunters are attacking this important species, which is in danger of going extinct.

Prairie dogs

Prairie dogs are a keystone species that live in the grasslands of central and western North America and support over 130 other species. They are ecological engineers, sustaining the health of parched grasslands by churning, aerating, and enriching soil as they form enormous and complicated underground colonies. They also provide food for coyotes, eagles, the endangered black-footed ferret, and other animals. Their digging promotes the growth of a variety of plants, which in turn supports more elk, bison, and other grazers. Additionally, jackrabbits, burrowing owls, and rattlesnakes find refuge in their tunnels. Woody plants may replace prairie dogs in their native grasslands habitat, drastically altering the ecosystem of the prairie.


Up to 90% of the world’s flowering plants depend on bees for reproduction, with the help of other pollinators, some of which, like hummingbirds, are also keystone species. They help generate the seeds, nuts, berries, and fruit that countless other species in ecosystems all over the world depend on in addition to pollinating the fruits, vegetables, and other crops that give people everything from food to clothes to fuel. Without bees, the food chain would be affected in a bottom-up cascade of ways. Despite this, important protections for bees like the threatened rusty patched bumblebee have not been implemented in the United States.


Sharks are keystone predators at the top of the food chain with a top-down effect on marine ecosystems all around the world. They prevent the spread of disease and manage prey populations by feeding on the sickest, frailest, and slowest animals. They also affect the local habitat: Sharks enable populations of herbivorous fish farther down the food chain to flourish by consuming predatory species like grouper in Caribbean reef ecosystems, for instance. These fish then graze on algae that would otherwise deteriorate coral reef. Keystone species also include some varieties of coral. One illustration is ivory tree coral, which may be found in the Caribbean, the Gulf of Mexico, and the waters off the Southeast United States and provide crucial habitat for more than 300 species. Krill, which is an essential food supply for numerous whales, seals, and seabirds in Antarctica, as well as mangrove-dwelling crabs are other ocean keystone species (which manage leaf litter and create burrows that improve underwater soil health).


The saguaro cactus, which is indigenous to the Sonoran Desert in the southwest of the United States and northwest of Mexico, is a keystone species that offers vital nesting locations for birds like red-tailed hawks and woodpeckers (the latter of which peck new nest holes each year, leaving old holes for other birds). Furthermore, these cacti are a significant food source. Bats, birds, and bees are fed by their flowering blooms, while numerous animals, insects, and other species rely on their fruit, which ripens when the desert is at its driest.

Other desert keystone species include the Australian dingo, which preys on a variety of herbivores (such as kangaroos) as well as predators in the middle of the food chain, like invasive red foxes and feral cats, and the desert tortoise of the Mojave, which excavates burrows that other animals rely on for protection from predators and the desert heat.

Boreal forest

The boreal forest, also referred to as taiga, surrounds much of the world’s northern latitudes just below the Arctic Circle. The imperiled Canada lynx, which depends on snowshoe hares for more than 75% of its winter diet, as well as other predators, use the snowshoe hare as a keystone prey species in the Canadian boreal. Keystone species in the boreal also include trees like aspen and willow, which are essential for the habitat of a wide variety of organisms, including lichens, fungi, insects, and birds, as well as plants like wild red raspberries, which are a vital source of food for animals like bees and bears.


The Arctic tundra, which covers the northern portion of the Northern Hemisphere, is a cold, treeless, and frequently snowy habitat that supports few plant and animal species. Lemmings, a small rodent species that experiences significant, cyclical population variations that have an effect on the entire arctic food web, are one of its most important prey species. Lemmings are a keystone species that provide food for predators like arctic foxes, snowy owls, and weasels. As voracious herbivores, they also have an effect on the quantity, quality, and makeup of the vegetation they consume. Dovekies are a keystone species that support polar bears and arctic foxes as prey while providing essential compost for the indigenous plants on a group of islands between Norway and the North Pole.

Tropical rainforest

Fig trees are an essential resource in tropical forests all over the world, providing year-round food for more than 1,200 different kinds of birds, bats, and other animals (including, critically, times of the year when other food resources are scarce). Keystone species include several creatures that wander through forests dispersing seeds in their droppings, which can later germinate and thrive. These include the southern Australian cassowary and the western lowland gorilla of Central Africa.