Loss of biological diversity

Nature is under severe stress worldwide due to the loss of biological diversity — precipitous declines in species numbers, in too many cases to the point of extinction.

For example, bird populations and insect populations have declined precipitously on a large scale. The North American bird population has declined by thirty percent since 1970. Insect populations have fallen dramatically worldwide. Bird declines can be directly tied to insect declines as 96% of terrestrial breeding birds rely on insects to feed their young.

Ecological systems (“ecosystems” for short) that lose biological diversity — like any complex system that loses its constituent parts — can’t function well. Failing ecosystems will not produce nutrients, water, air, and other products necessary for life on Earth. (See A deeper dive into ecosystems for more detail.)

The loss of biological diversity (“biodiversity” for short) is thus a global threat on par with climate change, although the consequences from reduced biodiversity have not yet manifested themselves as dramatically as climate change impacts.

Why Your Yard Matters

In our region, the main driver behind biodiversity loss is native habitat destruction due to urbanization, although climate change plays a role, too. Maryland is the fifth most densely populated state in the nation at 625 people per square mile. In Montgomery County, the population density is 2,543. Buildings, roads, and pavement have dramatically reduced the unbuilt land available for native habitat.

It is not feasible for rural Maryland alone to provide sufficient space for biodiversity. Conventional agriculture practices, such as mono-cropping and pesticide use, limit the land in rural areas where native species can live. As a result, in rural areas as in urban areas, the land available to native species is often fragmented and small. Isolating species in small land parcels reduces their population sizes. A population downswing can easily take a species below the critical population size necessary for survival.

In part, the solution lies in using our urban unbuilt spaces more wisely by planting them with native trees and plants. Native flora, even in urban areas, provides habitat for native fauna. The more unbuilt space we can plant with native plants, the more we connect otherwise fragmented green spaces.

In Takoma Park, the largest available unbuilt land is the yards around residential houses. That creates the opportunity to address biodiversity loss literally in our own backyards. Simple actions can turn our yards and streets into native habitat that provides native species with food, water, shelter, and space to complete their life cycles.

Since American yards contain more acreage than all our national parks combined, homeowners can potentially have a major impact on saving nature.

Why native plants

native:  a plant or animal that has evolved in a given place over a period of time sufficient to develop complex and essential relationships with the physical environment and other organisms in a given ecological community.

Rick Darke & Doug Tallamy
The Living Landscape

Native species foster biodiversity because they have vital interactions with so many other native species in an ecosystem. Species native to a specific area have evolved over millennia into an interrelated ecological system, an ecosystem. Countless evolutionary interactions among diverse native species underpin how well an ecosystem functions and can sustain itself.

For example, the larvae of the tawny emperor butterfly and the hackberry butterfly only eat the foliage of hackberry trees.  The tawny emperor eats older foliage while the hackberry butterfly eats new leaves.  If there are no or few hackberry trees, these two butterfly species will no longer be available to contribute to the food web and pollination in our area.

Non-native species have many fewer or no such species interactions.  Non-native species are like cogs that don’t mesh well with the other gears in the system

Ecosystems depend on their biodiversity to function, sustain themselves, and deliver the services upon which life depends.  “When we allow one species to die, we erase the web of relationships it maintained in life, with consequences that scientists seldom understand,” wrote the noted biologist, Edmund O. Wilson, “…we break many threads, and change the ecosystem in ways still impossible to understand.”

A deeper dive into ecosystems

People have various reasons for caring about nature enough to help preserve it: awe at its beauty; respect for life that has evolved on this planet along with us; feelings of well-being from being in nature.

Regardless of whether any of these reasons motivate you, we should all care about nature because it performs the biochemical processes that allow life to exist on Earth. Microbes, plants, fungi, and animals interact within a given ecosystem to provide the molecules that fuel the chemical processes of life–our life.

The most obvious example is photosynthesis that transforms solar radiation into molecules that can be transferred throughout the ecosystem, most notably through food webs. But other biochemical processes, such as decomposition, are equally important to life on Earth.

In the following graphic, Drs. Naeem, Duffy, and Zavaleta illustrate how the complex interactions among species in a terrestrial ecosystem translate into chemical reactions.

The biological interactions among soil microbes (heterotrophic prokaryotes), plants (photoautotrophs), fungi, and animals provide the molecules that fuel the chemical processes in a terrestrial ecosystem.

Note: The bottom panel (“Interaction Network”) illustrates the interactions in which energy and material are exchanged among the four basic types of species (animals, fungi, plants, and soil microorganisms) in a terrestrial ecosystem. The top panel (“Biogeochemical Pathways”) shows the various organic molecules supplied by each type of species and the chemical reactions through which energy and material are transferred.
Source: S. Naeem, J. E. Duffy and E. Zavaleta (2012). “The Functions of Biological Diversity in an Age of Extinction.” Science. Vol. 336. Issue 6087. Page 1403.

In short, we need nature’s ecosystems to produce, process, and transfer the fundamental building blocks of life. Below, Dr. Katharine Hayhoe warns us against thinking otherwise:

“..many of us still think and act as I did when I was young: mistakenly assuming that, were our planet’s ecosystems to collapse, we could miraculously persist without the air, water, and essential resources they provide. This perspective endangers us all. Climate change, pollution and biodiversity loss have escalated to crisis levels that threaten not just flora and fauna, but humanity itself. It’s our collective survival that’s at risk.”

Dr. Katharine Hayhoe, Scientific American, 2023

Studies over the past two decades have repeatedly found that greater biodiversity promotes more stable and efficient ecosystems (Naeem, Duffy, and Zavaleta, 2023). As human interventions in particular start to reduce biological diversity — both the number of species present, and the population size of each species — ecosystems reach a point where they begin to falter in their capacities to perform their life-sustaining functions, to process the materials and energy that power Earth’s life.

This makes intuitive sense. Ecological systems are complex products of evolution over millennia. Like complex yet resilient machinery, a few nuts and bolts can go missing without a noticeable impact. At some point, however, too many parts are gone for the system to work well.

In fact, ecosystems are more complex than this simple analogy to a machine suggests, and that complexity goes a long way toward explaining why greater biodiversity is so important (Tallamy, Bringing Nature Home, pgs. 38-44). It’s not the case simply that some species are “critical bolts” while others can be eliminated without impact. Rather, with more species in the ecosystem, there is more opportunity for other species to take over the critical functions (become the “critical bolts”), should some species disappear. Also, some species

• may handle stress and disturbances (e.g., wildfires, drought) better than others, thus making the ecosystem more resilient.
• may carry out those essential biochemical processes more efficiently, thus making the ecosystem more productive.
• fill ecological niches that would otherwise be open to invasive species that can upset the functioning of the ecosystem.