The planet’s environment is constantly changing, but the current pace and nature of these shifts create immense pressure on animal populations. A changing environment includes rising global temperatures, resource scarcity, habitat fragmentation, and the introduction of new pollutants or diseases. To persist, animal species must overcome these pressures. The methods employed fall into two categories: a long-term change to the species’ genetic makeup or a short-term, reversible adjustment by an individual organism.
Evolutionary Adaptation
Evolutionary adaptation represents a permanent, heritable change in a population’s traits that occurs across many generations. This process is driven by natural selection, where individuals with traits better suited to the new environment are more likely to survive and reproduce. Over hundreds or thousands of generations, these beneficial traits become more common, fundamentally shifting the species’ gene pool. This change is slow and requires the environmental pressure to remain consistent for a prolonged period.
A classic example is the peppered moth in England during the Industrial Revolution. Factory soot darkened tree trunks, making light-colored moths vulnerable to predators, while dark-colored variants had improved camouflage and survived. Another example involves the three-spined stickleback, which has shown changes in body armor over decades in response to warmer aquatic habitats. This genetic process requires sufficient genetic variation within the population and is irreversible within an individual’s lifetime.
Behavioral and Physiological Acclimation
The second mechanism involves short-term, non-genetic changes known as acclimation or phenotypic plasticity, allowing an individual animal to adjust within its lifetime. These responses are immediate and temporary, such as seasonal migration in response to temperature or resource availability. Animals may also exhibit behavioral shifts, like the California sea lion diversifying its diet and expanding its foraging range when preferred prey became scarce.
Physiological acclimation involves internal adjustments to maintain stability. For instance, an animal exposed to heat stress may alter its metabolism or blood chemistry to regulate body temperature. Mammals can increase thermal tolerance by adjusting fur density or temporarily allowing their body temperature to rise (hyperthermia) to conserve water. These plastic responses are crucial for immediate survival and are often the first line of defense, but they have limits and are reversed once the environmental stressor is removed.
The Speed of Environmental Change
The rate of environmental change dictates which strategy is most likely to succeed in preserving a species. Slow, gradual shifts, like those over geological timescales, provide enough time for evolutionary adaptation to occur. When change happens quickly, such as with modern climate change, species must rely on rapid behavioral or physiological acclimation to survive. However, the current pace of change often exceeds the capacity of both mechanisms.
Species that cannot acclimate quickly enough or whose plastic limits are exceeded face immediate population decline. For example, many bird species attempt to adjust nesting times to match earlier springs, but this phenological shift is often imperfect and reduces reproductive success. Rapid environmental change, such as warming temperatures, forces many species to shift their geographic ranges toward the poles or higher altitudes. If habitat fragmentation or a lack of genetic diversity prevents a species from evolving or acclimating rapidly, the risk of population collapse or extinction increases significantly.