Ecosystem Crises Interactions. Merrill Singer
example of ecosystem synergy is provided by black bears (Ursus americana). These omnivores eat various animals (including insects), though most of their diet is based on diverse plant foods. Their lives revolve around food acquisition, reproduction and offspring care, and hibernation. They have a keen sense of smell that enables them to locate various food sources. Pregnant black bears give birth to their young in dens, and mother bears lactate for about 3 months while living there (Alt 1989). During this period, females do not eat or drink, yet they produce more than 850 ounces of high‐fat milk. After emergence from the den—a part of the abiotic environment critical to bear survival—the composition of their milk changes as new milk production is based on the nutrients available in the diet rather than on fat stores (Oftedal et al. 1993; Iverson et al. 2001). Thus, black bears must consume large quantities of fat‐rich food before denning but may have more varied diets at other times of the year, depending on the season.
Research on black bears in New Mexico (Costello et al. 2001) found that key food items taken from the environment and used for energy and cell construction, as well as to produce and feed cubs, were flowering plants, grasses, juniper berries, squawroot, acorns, beechnuts, gooseberries, huckleberries, and blueberries. Blueberries, for example, provide energy in the form of sugar (15 grams for each cup consumed), as well vitamins and dietary fiber, while acorns are high in fats and carbohydrates. Notably, black bears are able to extract protein from flowering plants and grasses (Eagle & Pelton 1980). They are highly efficient berry‐eaters, capable of consuming up to 30 000 a day if they are available in their range; they can double their body weight in years when fruits are plentiful. They harvest berries rapidly, using their sensitive and flexible lips, and swallow them whole (Landriault et al. 2018). Research in Massachusetts (McDonald & Fuller 2005) found that postdenning milk produced for cubs during the spring was higher in fat (26.7% versus 18.2%) when acorns were abundant as compared with lean acorn‐production years. These plants acquire CO2 from the atmosphere and nutrients like nitrogen and phosphorous from the soil to build cells, grow, and produce leaves, nuts, and fruit. Bears were found to also consume a significant number of ants during part of the year. Both the bears and the primarily plant foods they consumed, as well as the ants, release CO2 back into the atmosphere as their bodies carry out cellular respiration. The waste excreted by bears provides energy and building material for bacteria and fungi living in the soil. These decomposers, in turn, release molecules like nitrogen back into the soil and atmosphere. The same occurs when bears and plants die. These resources are then available for plants and the cycling of energy and matter continues. Bears also disperse the seeds of the plants they consume. Some berry seeds pass through their digestive tracts unbroken and are able to germinate where they land. Each summer, black bears spread the seeds of their favorite berries throughout their home ranges, enabling berry movement to new patches and future bear food supplies.
These two examples, of course, are simplified illustrations intended to show some of the interconnections and synergies that make up an ecosystem. They are useful because, in the case of black bears, the arrival of European colonialists in North America led to a drastic drop in their numbers and range. Habitat loss (e.g., deforestation) and extensive hunting and persecution resulted in local extinctions and the disappearance of bears across significant sectors of their traditional range by the early 1900s. Subsequently, organized recolonization by conservation officers using bears from growing neighboring populations has been successful in many areas. The lessons of this example suggest the potential for species loss and habitat destruction, as well as the possibility of ecosystem restoration. Restoration of damaged peatlands is a more daunting challenge because of the time it requires: peat only forms at the rate of about 0.04 inches per year, so a 30‐foot‐deep peat bed takes 9000 years to form (Chalker‐Scott 2014). While degraded peatland ecosystems have been restored using sphagnum moss and mulch, CO2 continues to be released for a number of years through bacterial respiration during decomposition of the new organic matter.
2.3.1.2 Conceptualizing ecosystems
As an analytic concept, “ecosystem” was first used by the outspoken British botanist (and strong advocate of Freudian psychology) Arthur Tansley in 1935 (New Phytologist Foundation n.d.). Tansley, known as the father of British ecology, was the first president of the British Ecological Society and served as the initial editor of its Journal of Ecology. He developed the concept of the ecosystem to draw attention to traceable transfers and flows of energy (e.g., from the sun) and matter (e.g., nutrients, water) within specific geographic spaces. Ecosystems vary in size and complexity, and some scientists even view Earth as a single ecosystem. Ecosystem diversity references all the different habitats that exist on Earth, such as tropical or temperate forests, hot and cold deserts, wetlands, rivers, lakes and ponds, mountains and mountain valleys, caves, islands, shorelines, undersea kelp forests, coral reefs, hot springs, and deep‐ocean vents, plus many more. Matter and energy flow not only within ecosystems but between them as well (e.g., a river carries mater from land‐based to water‐based ecosystems), highlighting ecosystem interconnection.
Ecosystems are identifiable because they tend to maintain a natural balance among their component parts over time; that is, there is a state of dynamic equilibrium across their community of component organisms and a stability in the numbers of each species within them. This stability makes them recognizable even if identifiable changes occur (e.g., a beach ecosystem before and after a major storm). Ecological researchers have tried to develop general predictions about ecosystem community structure based on abiotic and biotic factors. Ecosystems, however, are not really static. They are impacted by various factors, including evolution, invasive species, salt intrusion, pollutants, overhunting, natural disasters, and global warming. Intrusive change in an ecosystem can be illustrated with the case of Walden Pond in Concord, Massachusetts, made famous by the environmentalist author Henry David Thoreau (2016). Walden Pond is what is called a kettle hole, a sediment‐bottomed shallow body of water. Created by glacial retreat, it is anchored by a beach and a surrounding wooded area. The detailed journal notes about the flora and fauna, weather, and seasons kept by Thoreau while living at Walden Pond from 1852 to 1858 have been used by modern scientists (Primack 2014; Stager et al. 2018) to show that because of climate change and other human influences, levels of phytoplankton have increased there, reducing water clarity, and ice on the surface now breaks up 2 weeks earlier than during his stay.
It has been found that ecosystems with higher biodiversity (a greater array of different lifeforms and genetic variations within species) tend to be more stable and to have greater resistance and resilience when faced with disturbances and disruptive events—an idea originally suggested by Darwin (Peterson et al. 1998). It is not easy in the short run to specify whether an ecosystem is disturbed (and could regain balance over time) or becoming a different, perhaps more degraded or simplified biotic/abiotic arrangement. Over longer periods of observation, however, it is evident that simplification occurs.
Ecosystems are different than habitats—another environmental term frequently used in this book. Habitats are the places where specific organisms live. Consequently, they exist everywhere on the planet, because organisms live everywhere. The Grand Canyon, for example, consists of multiple habitats, with cacti and warm desert scrub species living just above the Colorado River corridor, pinyon pine and junipers living above the desert scrub up to about 6000 feet above it, and abundant ponderosa pine living at even higher elevations. Other plant species and various animals also live in each of these habitats. Habitats exist in built environments as well, such as the tracks of the New York City subway, a habitat for the brown rat (Rattus norvegicus), as reflected in some of the popular names of this species (e.g., sewer rat, street rat). While ecosystem disruption refers to the loss of critical relationships, habitat disruption involves the loss of resources necessary for a species to live in a particular locale.
2.3.2 Biodiversity and the multitude of species
Another key concept of modern ecology that already has been mentioned several times is biodiversity. Earth is covered in organisms of diverse size, shape, and nature, and has been for billions of years, but all of them, both living and extinct, are related. Collectively, they form an extremely complex family tree. This is called the monophyly of all known life,