8.1 Intro to biodiversity and terrestrial ecosystems

Living things and the ecosystems they inhabit are affected by many environmental impacts, and contribute to many human benefits through ecosystem services. Food, fiber, building materials, medicinal materials, climate regulation, water purification, oxygen provision, links to physical and mental well-being, and the sacred – all of these things come to us from the planet’s living things and the ecosystems of which they are a part.  The UN Sustainable Development Goals for life on land and life on (fresh) water are the best direct matches for our topic here, but because of all the links to and from human activity, most of the other goals are also relevant.

Similarly, because the planetary boundaries are all different measures of the health of the planet, all of them are related to biodiversity and ecosystems – terrestrial, freshwater, and marine. Biosphere integrity is a specific match, as it gauges the overall health of organisms and their ecosystems. Other closely related boundaries include land use change, which monitors the modification of natural land cover – the plant component of ecosystems and the source of much of the habitat for the animal component. Freshwater change, modification of biogeochemical flows (especially nitrogen and phosphorus and the nutrient pollution they can cause), and ocean acidification all have direct effects on aquatic ecosystems. Climate change affects the other planetary boundaries and, as we will see, has increasingly harmful effects on biosphere integrity.

Vocabulary for biodiversity and ecosystems

A species is a particular kind of plant, animal, or other organism (species is both singular and plural). Definitions for “kind” vary, but one of the simplest is that a species comprises individuals of the same kind that can breed among themselves. This definition has a lot of gray area. Many animal species in North America are very closely related to species in Eurasia. They are physically separated and cannot breed with each other, but if they are brought together – for example by introduction of one group to the other’s continent – they may be able to breed successfully. But because they were unable to breed with each other, on their own, these would usually be considered different species. Some plant species are very difficult to differentiate because their breeding barriers are particularly poorly developed and, although they might have slightly different habitat preferences, when they meet each other, they hybridize along the zone of overlap.

A single organism from any species is not called a species. It is called an organism or an individual. Thus, the frog in accompanying image (Figure 1) is not a species. Rather, it belongs to a species. It is an individual Cope’s gray treefrog. Similarly, the plant that it is sitting on is not a species, but an individual of a species – a mapleleaf viburnum.

A population is a group of organisms of the same species that occupy the same space and time. Some populations are easy to delineate. All the individuals of a single species of fish – let’s use sunfish – in a single pond are a population. The red-whiskered bulbuls (a classy songbird) in Hanoi might be rather well delineated, because they prefer urban and suburban areas, parks, and gardens, and they might be much less common outside the city and its immediate surroundings. But other populations are delineated more for management purposes than because there is any clear separation of the individuals from other, nearby individuals. For example, park managers might refer to the population of impala in their park. But the impala don’t recognize park boundaries and probably move in and out of the park, although the number in the park might be somewhat consistent over time.

A community is the individuals of the plant and animal species (and fungi and other microorganisms, if those are also of interest) that share space and time. Some species may be quite closely adapted to particular conditions – specialists. Others may be tolerant of a wide range of conditions – generalists. The species in a community don’t share their habitat requirements completely – they simply overlap in this space and time.

We most often talk about communities with relation to the ecosystem they inhabit. The ecosystem includes abiotic – nonliving – elements including soil and water as well as the processes necessary to keep the ecosystem running – photosynthesis, decomposition, nutrient cycles, disturbance regimes such as fire cycles, etc. A forest ecosystem comprises the plants and animals of the forest, but also the landscape in which they are embedded. A forest community only encompasses the plants and animals.

A biome is a category of ecosystems. If you live near a forest, then your local forest is an ecosystem that is a single example of the forest biome. In places where natural landscapes are undisturbed, a single ecosystem could be quite large. But it is still an example of a biome. The boreal forest biome includes the forests across the northern lands of North America and Eurasia. Any single boreal forest is a small subset of the boreal forest biome (Fig 2).

Figure 2. Distribution of the boreal forest (or taiga) biome, with an inset of a Norwegian boreal forest ecosystem. Map: Mark Baldwin-Smith. Inset: Øyvind Holmstad. Both CC BY-SA from Wikimedia.

No single biome classification is accepted by everyone, but many of the major classifications are standard across lists of biomes. Some users group tropical and subtropical forests. Others subdivide tropical forests into wet, seasonally dry, and dry tropical forests. But in all cases, these are global categories that include many local ecosystems, often on multiple continents (Fig 3).

A watershed is a unit of land, and is described by topography and hydrology, not by species. A watershed is the land that drains to a single body of water – a river, a lake, or an ocean. The watershed of a small stream will be similarly small. Watersheds of large rivers are often called basins – for example, the Amazon basin. Figure 4 shows the major watersheds of the world, including watersheds that do not drain to an ocean but instead drain to continental interiors. The Great Salt Lake of North America, the Caspian Sea, Lakes Baikal and Balkhash of Central Eurasia are all examples of such land-locked basins.

In contrast to Figure 4, Figure 5 shows a specific level of watersheds in the US. If you look closely, you can see that the darker lines in Figure 5 include lines that follow the North American watershed lines shown in Figure 4. The US Geological Survey maps watersheds at many different scales in order to understand water movement and water availability both broadly and locally.

What is biodiversity and where does it come from?

Biodiversity is the diversity represented in living things. It can be considered in 3 separate ways.

• Species diversity is what most people think about when biodiversity is mentioned. The differences between a butterfly and a banana and a bat are easy to see.
• Ecosystem diversity is about the diversity of different kinds of collections of plants and animals and land resources: forests, wetlands, deserts, etc.
• Genetic diversity is about the diversity within a single species that comes about because of differences in genes: genes for digesting new foods, for running fast, for having spots or stripes, etc.

New genes happen rather quickly, through mutation, but most mutations are not helpful, and the mutations don’t persist as they are weeded out by natural selection. Natural selection occurs very simply, because individual organisms with genes better suited to a particular time and place have more offspring than less suited individuals. As a result, the genes that are better suited become more common, and the species becomes better adapted. Perfect adaptation never occurs because environmental conditions are never constant – something is always changing, and change means that new genes may become the better-adapted genes.

Species typically evolve fairly slowly, through natural selection. Occasionally, such evolution is more rapid, as when a flock of small birds survived a flight to the Galápagos Islands off the coast of Ecuador and, over time, became an entire suite of finch species, each adapted to feed on a different kind of food. These “more rapid” examples of species evolution still take time on the order of 1 or more millions of years – “rapid” is relative!

Ecosystems cannot evolve because they are collections of species and land conditions. But combinations of plants and animals can become more and less common. During an advancing Ice Age, as weather becomes colder, the combinations of plants and animals in a location changes, the precipitation regime probably changes, and the land itself changes as glaciers roll over it. When humans modify landscapes, similar changes may occur, for example after mining has disturbed the land.

Humans can cause the disappearance of populations – most of the wolf populations of the US have been gone for over a century. We can cause the extinction of species, and have apparently done so for thousands of years – the disappearance of many of the huge mammals of the last Ice Age – mammoths, dire wolves, and giant sloths – is believed to be due, in part at least, to overhunting by the humans of that time.^[1] We can eliminate local ecosystems by converting them to agriculture, building cities over them, flooding them with reservoirs, etc.

The biodiversity currently on the planet exists despite 5 major extinctions episodes in the planet’s past, including extinctions that are believed to have wiped out the majority of species on land and in the oceans. Recovery of planetary biodiversity from these extinctions took millions of years, and, in each case, the subsequent biodiversity was different from what came before. Researchers characterize our current time as beginning a 6th major extinction, due to the elevated extinction rates resulting from human activities including climate change.^[2]

Introduction to ecosystem services and valuation of ecosystem services

Just as humans define ecosystems, we define the benefits we derive from them. We value (or not) these services as a result of our own priorities. Ecosystem services are commonly divided into four categories.

• provisioning services provide us with goods – food, fiber, water, building materials, etc.
• regulating services help to maintain the world around us – trees that sequester carbon help to regulate climate; wetlands that can absorb waters help to reduce flooding.
• cultural services provide us with recreational opportunities, opportunities for reflection, inspiration for art, sacred places.
• supporting services underpin the other services – soil formation, nutrient cycling – they are the natural equivalents of keeping the lights on.

Obviously natural processes can provide services in more than one of these categories. In dry areas, springs may be sacred at the same time that they provide water. Trees provide building material and fiber, sequester carbon, provide recreational opportunities, and contribute to nutrient cycling.

Ensuring the continued provision of ecosystem services is often an aspect of conservation. It is complicated by the problem of valuing ecosystem services. In some cases, some measure of valuation is straightforward. The value of pollination to an almond producer might be measured in the market value of the almonds. But the same pollinators may also support other plant species that in turn support other pollinators and other wild animals – this additional value, if we deem it to be a value – is much harder to quantify.

We know, because the existence of support for nonprofit organizations demonstrates it, that people can value species and ecosystems they have never seen. This existence value is not fully measured by donations to nonprofit organization or tourism – many people may never act on their appreciation for this unseen nature. We can ask people how much they would be willing to spend to live closer to a national park or to have more hunting opportunities, or how far they would travel to have some experience with the natural world, but research tells us that these valuation methods often fail to produce useful results.^[3] Our inability to measure value for ecosystem services leads some to discount or dismiss their value entirely. In the case of common-pool resources (introduced in Chapter 1), which have no owners, difficulties with valuing ecosystem services may lead to their loss. Of course, common-pool resources of known value may also be lost, not because they are not valued but because they cannot be protected from those who would profit from their value.

A variety of approaches have been used to preserve biodiversity, ecosystems, and ecosystem services, with and without valuation. Recently, some governments have extended legal rights to Nature or to natural features. For example, in 2017, in the Te Awa Tupua (Whanganui River Claims Settlement) Act, the Parliament of New Zealand extended legal personhood to the Whanganui River. As with restorative agricultural practices (Chapter 7), however, the global balance is still towards loss of resilience, species, ecosystems, and ecosystem services.

Knowledge Check

Take a moment to complete the short quiz below to assess your understanding of this section. Read each question carefully and refer to the section content as needed. This quiz is not graded – it’s simply an opportunity for you to reflect on what you’ve learned and reinforce key concepts.