Life Cycles: A life cycle is the sequence of biological changes that occurs as an organism develops from an egg into an adult until its death. The life cycles of many species are synchronized with the life cycles of other species and the seasons. For example, many butterfly life cycles have evolved so that caterpillars hatch so that they can feed on particular plant species that grow at particular times of the year.  In some species, transitions between the stages in their life cycles can be triggered by changes in environmental conditions. For example, many plant species require seasonal exposure to cold temperatures for seeds to germinate. For species that rely on environmental cues for transitions between stages in their life cycles, recent changes in climate have altered when in the year those transitions occur.  This can cause problems, for example, if flowers boom earlier, before their pollinators migrate into the areas where the plants live.

Traits:  Traits are the characteristics of an organism, including how it looks (also called its morphology) and how it functions. These functions can be biochemical, physiological, or behavioral. Traits shape the way organisms interact with other organisms and with their environment. Traits are heritable if they are coded for in an organism’s genetic material (its DNA), enabling the traits to be passed from parent to offspring.

Life cycles and traits are affected by many Earth system processes and phenomena, including:

• Evolutionary processes that can change the heritable characteristics in interbreeding populations of organisms from one generation to the next.
• Species interactions, especially for species that depend on other organisms for food or shelter, or compete for food, space, or nesting sites.
• Climatic conditions, such as the amount of sunlight absorbed at different latitudes, temperature, and precipitation.
• Numerous other abiotic environmental factors, including soil quality, nutrient levels, wildfires, water acidity, and oxygen levels.

Humans have altered species life cycles and traits through a variety of activities, including:

• Fishing and hunting, which often removes large reproductively mature individuals from species populations, which, in turn, can favor the survival of smaller individuals that can reproduce.
• Habitat destruction, due to deforestation, agricultural activities, urbanization, the removal of water for human consumption, and/or the release of pollutants and waste into ecosystems. Many species must alter their life cycles or evolve new traits to survive in changing ecosystems.
• Activities that have caused global warming, such as the burning of fossil fuels, agricultural activities, and deforestation. Increased average global temperatures have altered seasonal temperature and precipitation patterns, as well as the distribution of snow and ice cover, which affects the life cycles of many species.
• Introducing invasive species that require native species to evolve to compete for food, water, or other resources.

Can you think of additional cause and effect relationships between biological life cycles and traits and other parts of the Earth system?

Visit the evolution, species interactions, and species population pages to explore more connections between the biosphere and global changes.

Investigate

Learn more in these real-world examples, and challenge yourself to construct a model that explains the Earth system relationships.

• Toxic river means rapid evolution for one fish species
• Warming to evolution
• Antibiotic resistant bacteria at the meat counter

Links to Learn More

• EPA Climate Change Indicators: Leaf and Bloom Dates
• USA National Phenology Network