In any ecosystem, species can be thought of based on their relative influence. While some species are notable for their sheer numbers or the powerful effect they have on their environment, most are not. These other organisms, which can be called secondary species, are not the most abundant or influential but still perform functions that contribute to the overall structure and stability of their habitat.
Their presence ensures that various ecological processes continue, even if their individual impact is not immediately obvious. These species occupy a middle ground of influence, more numerous than the rarest organisms but less populous than the most dominant ones. Their value is found in their collective contributions to the system’s resilience and function.
The Ecological Niche of Secondary Species
One of their primary roles is serving as a consistent and alternative food source for predators. When the main prey of a carnivore becomes scarce due to disease or migration, predators can switch to consuming these secondary populations. This dietary flexibility can prevent a predator’s population from crashing, maintaining balance in the food web. For example, while coyotes might prefer rabbits, their ability to subsist on rodents, birds, and even insects during lean times demonstrates their importance.
These organisms also contribute to population control. Many secondary species are insectivores, consuming large quantities of insects that could otherwise damage plant life or spread disease. Certain species of bats and birds, for instance, may not be the most numerous animals in a forest, but their nightly foraging helps regulate mosquito and moth populations. This allows dominant plant species to thrive without excessive pressure from herbivorous insects, supporting the ecosystem.
Furthermore, many secondary species are involved in nutrient cycling. A wide range of organisms, from beetles to fungi, are decomposers that break down dead organic material like fallen leaves and wood. This process releases nutrients back into the soil, making them available for plants to absorb. Other species contribute through actions like pollination or seed dispersal, ensuring that plants can reproduce and colonize new areas.
Position in the Ecosystem Hierarchy
The role of a secondary species becomes clearer when compared to other ecological classifications. Ecosystems contain dominant species, which are the most abundant organisms or have the highest total biomass. A forest might be defined by a particular type of tree, like the oak in an oak-hickory forest, which dictates the environment by creating the canopy and influencing soil conditions.
Their impact is more proportional to their numbers, unlike that of a keystone species. A keystone species has a disproportionately large effect on its ecosystem relative to its population size. The classic example is the sea otter, which, by preying on sea urchins, prevents the urchins from destroying kelp forests. The otter is not the most abundant creature, but its actions shape the entire community.
Secondary species do not possess this level of influence. Their removal would not cause the immediate and widespread collapse often associated with the loss of a keystone species. Instead, their importance is more subtle, contributing to the overall stability and richness of the ecosystem. They represent a different type of ecological significance, one based on steady contribution rather than transformative impact.
Consequences of Their Removal
The disappearance of a secondary species can initiate a slow cascade of negative effects throughout an ecosystem. The loss often creates vulnerabilities that are not apparent until the ecosystem is placed under stress, such as from a drought or the outbreak of a disease. These species provide a level of redundancy and support that helps buffer the community against such shocks.
Consider a wetland where a particular species of frog is a secondary predator, primarily consuming various insects. If this frog were to disappear, the insect populations it once controlled could expand, potentially harming the native plants. At the same time, predators that relied on the frog as a backup food source, such as herons or snakes, might struggle to find enough food, especially during seasons when their primary prey is less available.
The removal of one component, even one that does not seem significant, can weaken the entire structure. The loss of a secondary species may not cause the ecosystem to collapse, but it can lead to a simplified and less resilient environment. The biodiversity of the habitat decreases, and with it, the ecosystem’s capacity to perform certain functions, such as nutrient cycling or pest control, is diminished, leaving it more susceptible to future disturbances.