Our Environment – Life on Land

The principles of life on land are not that different from life in the sea.  It is believed that life began in the sea but, the creation of continents and islands, new habitat was available for colonization.  However, the creatures who would colonize land would have to have different characteristics than those in the sea.

A limiting factor for the producers in the sea was light.  Sunlight is the energy that fuels the process of photosynthesis.  Thus, the producers had to either live in shallow water or be able to stay near the surface of the sea in order to function.  For MOST locations on land, sunlight is not the issue.  In fact, in some locations, too much sunlight can be an issue.  You need sunlight, water, and carbon dioxide to photosynthesize – and on land, water would be the hardest to obtain.  Many land creatures actually still live in water part time.  There are rivers, lakes, and streams crossing over the landscape that can provide suitable habitat for both producers and consumers.  However, most of the landscape is not water and photosynthesizing plants – like trees, grasses, and shrubs – developed root systems to absorb water from the ground.

Another player in this game are the swirling ocean currents.  As they rotate past the polar regions of the world, they become colder.  As the cold currents pass land, they lower the humidity and produce less rainfall.  Drier conditions meant plants had to adapt to both the issue of over evaporation and sufficient groundwater to support them.  Desert plants have done just that.  Often along mountain ranges the mountainside closest to the ocean, or warm currents will produce the greatest amount of precipitation.  While the opposite will be drier and more desert like.  The producers who live on each side of the mountain will be different due to this.  Landscapes near warm ocean currents are humid and rainfall is high.  Here the landscape is lush and green with some of the highest plant diversity found on the planet.

Land dwelling consumers follow suit.  They must first be able to deal with the amount of sunlight, temperature fluctuations, and humidity as the planets do.  Then the primary consumers – those that feed on the producers – must be able to feed on the plants that have adapted to that area.

These climate conditions have formed what biologists call biomes – ecologically unique ecosystems.  Examples of biomes are deserts, grasslands, alpine forests, hardwood forests, swamps, marshes, and more.  Each possesses their unique plant and animal communities.  And – like the systems found in the sea – they are constantly changing.  Life on land has to deal with the seasons of the year more than those in the oceans do.  Prey evolve to defend themselves from predators.  Predators evolve to overcome these new defenses.  Some species are very successful, others have gone extinct.  Though large-scale climate changes – such as ice ages and warming periods – impact life in the sea, they tend to be more impactful for life on land.

Biogeography is the study of how creatures disperse across the landscape (or ocean), meet barriers, and define their biological range.  Some creatures have large areas where they are found – such as seagulls, squirrels, and raccoons.  These are called cosmopolitan species.  Others have very small ranges – such as the marine iguana, Komodo dragon, and kangaroos – and are referred to as endemic species.  There are many plants and animals that dispersed across North America and can be found on both coasts.  Others are only found in one small area of the country.  In our next article we will introduce one species that has dispersed across the entire planet – humans.