Bee activity on robusta coffee blossoms at the Poomaale Collective

Keystone species are species that define an entire ecosystem. They have a disproportionately large impact on the structure and functioning of the ecosystem they belong to relative to their abundance. Without them, the ecosystem could be very different or not even exist. Like a keystone keeps an arch together, keystone species hold the entire ecosystem web together, thereby maintaining the balance and stability of the ecosystem and exerting a strong influence on the diversity and distribution of other species within the community.

The concept of keystone species was first introduced by ecologist Robert T. Paine in 1969 when he conducted studies in intertidal ecosystems and observed that removing a specific predator species (the ochre sea star) led to a dramatic shift in the composition of the entire ecosystem. Certain prey species (such as mussels) dominated the area without the sea star’s presence, leading to a decline in overall diversity and a less resilient ecosystem.

Characteristics of Keystone Species

Keystone species possess several defining characteristics that set them apart within ecosystems, the foremost being the scale of their influence with respect to their population size. These species are also known to be irreplaceable within that particular ecosystem. Their ecological functions are distinct from other species in the same ecosystem. This uniqueness often results in low functional redundancy, meaning that no other species can fully compensate for their role.

The presence of keystone species helps maintain the stability and balance of the ecosystem. Their activities regulate the populations of other species, preventing any one species from becoming overly dominant. On the other hand, they have a cascading effect on the rest of the ecosystem. When keystone species are present, their impact ripples through the food web, affecting the abundance and distribution of multiple species. If they are removed, these cascade effects can lead to significant shifts in the ecosystem. They exert top-down control in the ecosystem, meaning their influence starts from the highest trophic levels and cascades down through the food web.

Many keystone species are known to be predators that regulate the populations of their prey, preventing overgrazing or overpopulation that could disrupt the ecosystem. Some keystone species are ecosystem engineers, meaning they modify their habitats in ways that broadly affect the ecosystem. For example, beavers build dams that create new wetland habitats and influence water flow.

The unique functions and far-reaching effects make keystone species essential components for the survival and sustainability of various ecosystems.

Common Misconceptions About Keystone Species 

Keystone species defy conventional notions of abundance or size within ecosystems. Their significance lies not in population numbers or physical stature but in the profound impact of their ecological function on the entire ecosystem. Their presence or absence can make or break an ecosystem. An important thing to note is that keystone species are not universal symbols. The ecosystem in question helps define which species is the keystone. A keystone species in one habitat might not hold the same role in another; its identity depends entirely on the unique characteristics of its environment.

The role of keystone species extends beyond predators, as herbivores can also hold this crucial status. Herbivorous creatures also carry keystone potential. They define the limits of vegetation and contribute to their ecosystems’ physical and biological characteristics. For instance, Indian elephants are recognised as keystone species in the Western Ghats forests due to their profound impact on vegetation and habitat structure. In the African savannah, elephants act as keystone species by influencing vegetation and shaping the landscape. 

Even prey species can be keystone, such as the Nilgiri tahr in the Southern Indian hills or the sea otter in kelp forests. Furthermore, mutualist species working in tandem can collectively serve as keystone species.

Examples of Keystone Species in India

Keystone species can range from plants to fungi to giant mammals.

Some examples of keystone species in the Indian subcontinent include the Asian Elephants (in India – Indian Elephants), found in the forests of southern and north-eastern India. They shape the structure of forests by creating clearings, dispersing seeds, and maintaining pathways. They also help maintain the health and diversity of the ecosystem by their browsing and seed dispersal activities. Another example is the Bengal Tiger, found across diverse geographical locations in India. Being apex predators, they regulate prey populations, maintaining the balance of the food web. Owing to their iconic status, the Indian Elephant and the Bengal Tiger also fall under the category of flagship species.

In southern India, the Nilgiri Tahr, an endangered mountain goat species, is a keystone species in the Nilgiri Hills. Its browsing behaviour shapes the structure of the grasslands and impacts the vegetation, influencing other species that rely on these habitats. Termites, often overlooked as pests, are a typical example of keystone species. They feed on dead plant material, wood, etc., which helps clean up habitats and cycle nutrients through ecosystems. They improve soil properties and make it easier for water to move through the ground – all of which help the plants in the vicinity to grow. In addition, the mounds that termites collectively create can go up to as tall as 9m and as wide as 30m! These mounds are not just used by termites. From big cats chilling on the gently sloped mounds to tiny birds making them their nests – almost all forest creatures have a place in and around them.

Role of Keystone Species in Biodiversity Conservation

Conservation efforts may inadvertently disrupt these delicate balances without thoroughly understanding their ecological functions, leading to unintended consequences. Identifying and prioritising keystone species allows conservation efforts to focus on protecting species that have the most significant impact on ecosystem health. By safeguarding keystone species, conservationists can indirectly protect numerous other species that depend on them. Furthermore, negative cascades that can lead to species declines, habitat degradation, and ecosystem collapse can be prevented.

Knowledge of keystone species can aid in developing strategies to manage and control invasive species that could disrupt native ecosystems. Ecosystems with intact keystone species provide essential ecosystem services, such as pollination, seed dispersal, water purification, and carbon sequestration. Conserving these species ensures the continued provision of these services.

Many keystone species are also economically important, whether for ecotourism, agriculture, or other industries. A comprehensive understanding of these species enables the development of sustainable management practices that benefit both ecosystems and human livelihoods. Conservation efforts focused on keystone species contribute to ecosystems’ long-term health and resilience. Conservationists can address broader ecosystem health by addressing the factors that support these species.

A thorough understanding of keystone species is fundamental for successful ecosystem conservation and sustainable development of landscapes, such as that of Beforest Collectives. Their roles, interactions, and impacts are central to maintaining the integrity and sustainability of ecosystems, making informed decisions, and ensuring the well-being of both species and habitats.