Causes of Earth's Declining Biodiversity

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The Stockholm Resilience Center in Sweden has measured and quantified nine of the major environmental threats to our planet. The purpose is to define the boundaries within which humans can safely continue to thrive and develop for generations to come without irreversible impacts on the environment causing negative feedbacks to human survival (Figure 24).

Throughout Healing Earth, we will explore all nine of these environmental threats. For now, we concentrate on biodiversity, which happens to be the most severely threatened feature of the environment. What are the main causes of Earth’s declining biodiversity and what can be done about it?

Figure 24: Beyond the Boundary. The inner green shading represents the proposed safe operation space for humans within nine planetary system threats. The red wedges represent an estimate of the current position for each variable. The boundaries in three systems (rate of biodiversity loss, climate change, and human interference with the nitrogen cycle), have already been exceeded, with the rate of biodiversity loss being exceeded most profoundly. 1

The 2005 MEA reported that changes in biodiversity due to human activities were more rapid in the past 50 years than at any time in human history, increasing the risks of abrupt and irreversible changes to ecosystems.

Anthropogenic (human-induced) modification and destruction of habitat via land use is the most severe driver to loss of biodiversity. Land use transforms the physical environment, rendering it unsuitable to support high biodiversity (Figure 25). Different types of land use and its consequences include conversion of land to agriculture, urbanization, deforestation, desertification from over-grazing by livestock, infrastructure development (i.e., pipelines, construction of roads and railways) and introduction of toxins and other pollutants.

Figure 25: Examples of anthropogenic habitat destruction - a. terraced agriculture; b. clear-cut logging; c. deforestation; d. over-grazing in dry lands. 1

Habitat loss is the primary cause of decline for species and populations because it removes the flora and fauna that each species requires for life. When more and more land use occurs within areas of high species richness, loss of biodiversity is greatly exacerbated and species extinctions increase.

Habitat fragmentation occurs when land use activities divide and separate previously continuous habitats within a landscape. The effects of habitat fragmentation tend to be most severe for species that have large area requirements, poor dispersal ability, naturally unstable populations, or low population growth rates.

Looking Ahead

You will learn in the upcoming Biodiversity and Spirituality section that many biodiversity hotspots contain lands preserved by Indigenous People as sacred lands.

The major cause of habitat loss on the planet is agriculture and its expansion. The demand for food security – and recently, for biofuel – has led to agricultural expansion that accounts for >30% of conversion of land from diverse ecosystems to primarily large scale growth of monoculture crops.

According to the Food and Agricultural Organization of the United Nations (FAO), 40% of the Earth’s forest cover has been lost due to human impact, primarily through deforestation for conversion to agriculture. At current rates of deforestation, by 2050 another 10–20% of the Earth’s grassland and forestland will be converted to agriculture.

Figure 26: Examples of invasive species: a. Emerald Ash Borer, introduced to the United States from Asia; b. Burmese Python, introduced to the Florida Everglades via release by pet owners; c. Sea Lamprey, invaded the US Great Lakes from Atlantic Ocean when St. Lawrence Seaway was built; d. Kudzu, introduced to the US from Japan. 1

In addition to land loss, changes in optimal environmental conditions due to climate change are responsible for the extinction of countless species. Introduction of invasive species (Figure 26) have also led to the local extinction of native species that could not compete for resources with rapid-growing invaders.

One could argue that humans are the most destructive invasive species, in that our influence is expansive and affects life in all biomes on Earth. As a result of human activities, extinction rates are now 1,000 – 100,000 times higher than the natural rate of extinctions, referred to earlier as the Anthropocene Mass Extinction. In contrast to other extinctions, which occurred over long periods of geologic time, this sixth extinction event is occurring much more rapidly.

It is believed that around 10,000 species have gone extinct within the last 100 years. According to Conservation International, one third of all amphibian species are threatened with extinction, as well as nearly half of turtles and tortoises, one in eight bird species, and one in four species of mammal. The World Conservation Union reports that 52% of known insect species, and 73% of known flowering plants are in danger of extinction. In addition, overfishing and climate change are putting countless marine species at risk.

Questions to Consider

  • What type of terrestrial biome do you live in?
  • What aquatic ecosystem is closest to where you live?
  • Imagine that you had a chance to change a parcel of land near where you live in order to benefit your community. How would you change it? Would this change improve biodiversity where you live, or diminish it? Explain.

To slow the rate of biodiversity loss on Earth, broad cooperation is needed from industry, agri-business, governments, non-governmental organizations, communities, and individuals around the world. However, without sincere recognition of the moral value of biodiversity, cooperation will be difficult to sustain when economic and political pressures push against the good intentions of people and institutions. An ethical perspective is necessary to direct and strengthen our scientific knowledge of biodiversity toward a healed Earth. This is the subject of our next section.