The question of why some animal species flourish while others face extinction is central to modern ecology. Animals that thrive are typically classified as “Least Concern” (LC) by the International Union for Conservation of Nature (IUCN), meaning their populations are large, stable, or growing. Their success is a result of biological strategies that enable them to navigate the rapidly changing world, particularly landscapes reshaped by human activity. Examining the common threads among these successful species uncovers the underlying mechanisms that allow them to succeed where more specialized species fail.
Adaptability in Environment and Diet
A defining characteristic of thriving species is their flexibility, making them “generalists” rather than specialists. These animals possess a broad ecological niche, allowing them to exploit resources and habitats inaccessible or unusable to others. This adaptability is most evident in their dietary habits, often being omnivores that can switch between plant and animal matter depending on availability.
The raccoon, for example, is a dietary generalist that consumes everything from fruits, nuts, and insects to discarded human food waste, enabling it to inhabit diverse areas from forests to dense urban centers. This flexibility is paired with a high tolerance for varying environmental conditions, including temperature extremes and different levels of humidity. The coyote’s range has expanded across North and Central America due to its ability to survive in environments ranging from deserts and grasslands to suburban neighborhoods. This adaptability allows generalists to establish populations across vast geographical areas and quickly colonize human-modified habitats.
Effective Population Dynamics
The resilience of successful species is built upon reproductive strategies that allow for rapid population rebound and growth. Species that thrive often lean toward an r-selection life history, which emphasizes high reproductive output rather than intensive parental care. This strategy is characterized by a short generation time, early sexual maturity, and frequent breeding cycles.
The house mouse exemplifies this strategy. A female house mouse can reach sexual maturity in as little as six weeks and has a gestation period of 19 to 21 days. She can produce multiple litters annually, typically yielding six to eight pups per litter, and can mate again immediately after giving birth. This high output means populations can quickly recover from localized disasters or high rates of predation, ensuring the species’ abundance is maintained.
Mastering the Ecological Niche
Thriving animals actively exploit human environments, utilizing the “anthropogenic” ecological niche. Many of these species exhibit synanthropy, meaning they benefit from living in close association with humans and infrastructure. Urban coyotes, for instance, have higher survival rates in residential areas compared to rural areas, partly because metropolitan settings offer protection from the hunting and trapping pressure found in the countryside.
Coyotes in urban settings also demonstrate competitive superiority over smaller carnivores, regulating the populations of mesopredators like raccoons and skunks. The availability of anthropogenic food sources, such as pet food left outside or discarded food scraps, allows urban coyotes to thrive with smaller home ranges than their rural counterparts. This strategic use of human-provided resources, coupled with a behavioral shift toward nocturnal activity to avoid human interaction, solidifies their position as urban predators.
Genetic Diversity and Disease Resistance
The long-term success of abundant species is underpinned by a robust and diverse gene pool, which acts as a biological buffer against environmental threats. High genetic diversity means a population possesses a wide array of different alleles, or gene variants, offering a greater chance that some individuals will carry traits resistant to novel challenges. This is particularly important for resistance to disease and parasites, as a genetically varied population is less likely to be wiped out by a single, rapidly spreading pathogen.
In contrast, endangered species often suffer from a “genetic bottleneck,” a sharp reduction in the gene pool that leaves them highly susceptible to inbreeding depression and vulnerable to a single disease outbreak. The large, widely distributed populations of thriving generalists ensure continuous gene flow across their range, allowing them to adapt to evolving threats and environmental pressures.