Before discussing the impacts of alien plant species, it is important to mention the egocentric view that exists around the word "impact."  Too often the word tends to be directed at ourselves with regard to how invasive weeds impact our lives.  There is no question that the spread of invasive plants affects both aesthetic and practical aspects of our lives.  The question of impact though, can be viewed from another direction, "What role do humans play in the distribution of non-native plant species, and how does the establishment of those invasive species impact biodiversity?"  It can be argued that our actions have affected the quality of biodiversity, and therefore, by our own hand we suffer the consequences of unhealthy ecosystems in both personal and economic loss.

This unit examines the dramatic impact of alien invasions upon biodiversity, and then looks upon the consequences of our actions that brought these invasions to our lands.  Why is Biodiversity important?  The renowned biologist, E. O. Wilson, coined the term "biophilia" to describe the feeling that most people have for the value of great numbers of species.  Species richness, or variety, is key to healthy environments, and healthy environments provide people with many values.  Aesthetic values (the value of beauty and wonder) also extend to include spiritual value (where the environment plays a role in our cultural and religious traditions) and our ethical values (our value of life and the fact that it simply exists).  Biodiversity is also valued by humans for more practical reasons.  The greater the number of species, the greater the diversity, and so by extension, the more opportunities for humans to obtain food, medicines and materials that sustain our lives. Richness of species also improve the quality of abiotic resources.  The energy flow within ecosystems, including nutrient cycles, carbon and nitrogen cycles, and the hydrologic cycle, are fueled by biodiversity.  The air we breath, the water we drink, and the soil for our crops are directly affected by a healthy ecosystem, this web of richness, this diversity of life.

Invasive plant species affect biodiversity by altering habitats through competition for light, water, nutrients and space.  As we saw in the previous Invasive Unit, non-native plants introduced to a new habitat frequently arrive without limiting factors of competition, herbivores, or disease that kept their numbers in check within their native habitat.  Without these natural limiting factors, invasive weed species are able to quickly monopolize the landscape.  The pressure of this competition is often too much for the native plant species, and so, the health and biodiversity of the habitat declines.  The impact does not end with the weakened native plants, for in a healthy ecosystem, all life is connected.  Herbivory refers to the animals and insects that feed on plants.  Those herbivores may find fewer and unhealthy plants, leading them to move from an area or find their own health affected.  Diseases that are naturally occurring may benefit from the weakened plant community in the short run, quickly moving through their weakened host, decimating the population and making way for the spread of invasive plants.  The ripple affect of an invasive plant can quickly diminish biodiversity; approx. 400 of the 950 species listed as threatened or endangered are at risk specifically because of the introduction of non-native plants and animals, leading to the second major cause of lost biodiversity in North America.

In the opening paragraph, it was suggested that the impacts of invasive weeds to our lives is by our own hand.  Indeed, the leading cause of biodiversity loss is from human actions which reduce and destroy habitat through development.  Since we have seen the majority of invasive weeds are best able to benefit from these disturbed soils around our developments, it is not surprising to see that alien species, by our own hand, have become the second leading cause of habitat destruction and the diminishment of biodiversity around the world.

 

Links to Activities

Your Curriculum - The following lesson fit naturally within your regular classroom ecosystems curriculum.  They extend the Invasion Unit, allowing students to see firsthand how exponential growth patterns diminish biodiversity, upsetting the balance of life, and hence, impacting our lives economically and spiritually.

Alien Populations EXPLODE!
Aliens In The Web - Upsetting the Balance

Glossary

 The glossary at the end of each lesson provides additional keywords that can assist you with background information for the integration of concepts similar to your own curriculum.