The Ecology Book

by DK

  The overfishing problem is now compounded by climate change and pollution, which are also affecting ocean ecosystems. The consequences could be dire. If global warming continues, it will cause higher ocean temperatures, sea ice will melt further, and wind and ocean current patterns will change. As a result, nutrients from the upper ocean will be transferred to the deep ocean, starving marine ecosystems and reducing photosynthesis by phytoplankton, which serve as the base food in the ocean food chain. Within three centuries—by 2300—the world’s fisheries could be 20 percent less productive, and between 50 to 60 percent less productive in the North Atlantic and western Pacific. The predictions, calculated in 2018 by scientists at the University of California, Irvine, are based on extreme global warming—a 17°F (9.6°C) increase, but their models show that it is a possibility.

  Large-scale fishing operations disturb the balance of marine ecosystems in various ways, depleting the target fish species, upsetting the food chain, and damaging the marine environment.

  “I didn’t take the fish from the goddamn water.”

  John Crosbie

  Finding new solutions

  Seafood consumption has risen from 21.8lb (9.9kg) per capita annually in the 1960s to more than 44 lb (20 kg) in 2016. Global demand is predicted to reach around 236 million tons by 2030. Aquaculture, the farming of fish and seafood, has begun to meet much of the demand and has the potential to reduce the pressures on wild fish stocks. However, aquaculture has its own problems. Nutrients and solids added to the water can cause the environment to degrade. The buildup of organic matter from many fish in a farm can change the sediment chemistry, which has an impact on the surrounding water. Fish may escape, introducing alien species or diseases into the outside freshwater or marine environment.

  While fish farming helps meet demand, overfishing still poses huge dangers for the health of the world’s marine ecosystems, and the economic future of many nations. The Canadian moratorium severely disrupted the economy and culture of Newfoundland and neighboring maritime provinces. To avoid such crises, more governments will have to develop sustainable fishing practices, and protect the health of ecosystems and fish stocks.

  A deep-sea salmon farm, built in China, begins its journey to Norway. The huge, semi-submersible cylinder aqua-farming platform is designed to produce 1.5 million salmon a year.

  Effects of pollution

  Thick blooms of phytoplankton appear in red on this satellite image of the Gulf of Mexico. Bacteria break down decaying algae, releasing CO2 and absorbing essential oxygen.

  Two main types of pollution damage marine ecosystems. Runoff from fertilizers is a common problem: the nitrogen and phosphorus that many contain produce algal blooms (overgrowths of algae, or phytoplankton), which later die. As they decompose, they take up oxygen, creating a “dead zone” in the water that cannot sustain life. Because fish must leave such water or perish, juvenile fish living close to the shore are at risk before they move into the open ocean. In 2017, the annual dead zone in the Gulf of Mexico was more than 8,500 sq miles (22,000 sq km). Plastic pollution is another threat because fish eat it and get caught in nets and debris. Estimates suggest there are more than 5 trillion pieces of plastic in the ocean, with over 8 million tons added each year. If plastic pollution continues unchecked, the volume of plastic in the ocean will exceed that of fish by 2050.

  See also: A holistic view of Earth • Pollution • Human devastation of Earth • Sustainable Biosphere Initiative

  IN CONTEXT

  KEY FIGURE

  Ryan M. Keane, Michael J. Crawley (1949–)

  BEFORE

  1951 The International Plant Protection Convention is set up to prevent the introduction and spread of pests of plants and plant products as a result of international trade. It is adopted in many countries.

  1958 The Ecology of Invasions by Plants and Animals by British ecologist Charles Elton is the first book to be published on invasion biology.

  AFTER

  2014 Studies of some of the “world’s worst” invasive species by ecologists at Queen’s University, Belfast, and Stellenbosch University, South Africa, reveal that the ecological impacts of these species could be predicted from their behavior.

  Some of the greatest damage to ecosystems is caused by invasive species. These are plants, animals, or other organisms that are not native to an ecosystem but introduced largely through human action, either deliberately or by accident. They can become competitors, predators, parasites, and hybridizers of native plants and animals, ultimately threatening the survival of those species.

  The harlequin ladybug is the world’s most invasive ladybug. In the UK, where it was first seen in 2004, it is reportedly responsible for the decline of seven native ladybug species.

  The rise of the rabbit

  One of the most notable species invasions has been that of the European rabbit in Australia. It began in 1788, when 11 ships landed at Botany Bay from Britain, to establish the first Australian penal colony. On board the “First Fleet,” along with more than 1,000 people, including convicts and emigrants, were six European rabbits, brought along for food.

  By the 1840s, rabbits had become a staple food in Australia, and were contained within stone enclosures. All this changed in 1859 when a settler, Thomas Austin, imported 12 pairs of European rabbits and released them on his estate near Geelong in Victoria. Twenty years later, rabbits had migrated to South Australia and Queensland, and then in the next two decades to Western Australia. By 1920, the rabbit population was 10 billion.

  Rabbits appear to be innocuous creatures, but they have wreaked havoc on Australia’s native species, competing with them for resources such as grass, herbs, roots, and seeds, and degrading the land. They become particularly troublesome during a drought, when they eat anything they can find in order to stay alive.

  There have been several attempts to control the feral population, from rabbit-proof fences stretching more than 2,000 miles (3,200 km) to the more successful introduction of the myxoma virus and the rabbit calicivirus, in 1950 and 1995 respectively. The resulting disease has proved the most effective way of controlling their numbers and protecting native species.

  Since their arrival in Australia, rabbits have spread throughout the country. They have contributed to the decline of many native plants and animals, and may have caused several small mammals to go extinct.

  The secrets of success

  As invasive species have spread throughout the world, scientists have tried to determine what makes some of these species so successful, and how to control them without accidentally introducing additional ecosystem problems. Despite being hampered by the lack of comparative data on those invasive species that fail to succeed, scientists have developed a number of theories to explain the success of certain species in non-native environments, including the resource availability hypothesis, the evolution of increased competitive ability hypothesis, and the enemy release hypothesis.

  In general, species success depends on a variety of genetic, ecological, and demographic factors. The resource availability hypothesis, first proposed in 1985 by the ecologists Phyllis Coley, John Bryant, and F. Stuart Chapin, argues that an invasive species thrives because it is already well suited to its new environment and can take advantage of any surpluses in resources. The evolution of increased competitive ability hypothesis, published by ecologists Bernd Blossey and Rolf Nötzold in 1995, suggests that invasive plants facing fewer herbivores in their naturalized environment can allocate more resources to reproduction and survival and so out-compete the native species. The enemy release hypothesis, set out by ecologists Ryan M. Keane and Michael J. Crawley in their 2002 article “Exotic Plant Invasions and the Enemy Release Hypothesis,” argues that the invasive species has fewer enemies in its naturalized environments, and so can spread farther. The reality is that the success of invasive species is likely due to many mechanisms working together.

  “We are seeing one of the great historical convulsions in the world�
�s fauna and flora.”

  Charles Elton

  Plant invaders

  One plant that appears to support multiple hypotheses about the success of invasive species is garlic mustard (Alliara petiolata). Native to Europe, western and central Asia, and northwestern Africa, it was brought to North America by early settlers to use in cooking and medicines, and rapidly spread. Continued infestation has affected the growth rate of tree seedlings and reduced the native plant diversity, leading to changes in the forest ecosystems invaded.

  In its native range, garlic mustard is consumed by as many as 69 insect species, but none of these is present in North America. This lack of predation and the plant’s invasive success provide support for the enemy release hypothesis. Garlic mustard also successfully competes with native plants for resources, fulfilling the resource availability hypothesis. The plant even exudes secondary compounds that may “attack” native plants by inhibiting their germination and growth. This supports the “novel weapons” hypothesis, proposed by ecologists Wendy M. Ridenour and Ragan M. Callaway in 2004, which posits that invasive species have biochemical weapons that give them a key advantage over native species.

  Garlic mustard is highly invasive in North America, inhibiting other plants. In its native habitat, it is considered an attractive wildflower, although it can have a strong smell.

  The art of control

  Successful invasive species are extremely difficult to control and almost impossible to eradicate. If the species is a plant, the most obvious way to remove it is to pull it up or cut it down, but such methods are highly labor-intensive, especially over a wide area. The use of chemicals to destroy invasive species is often successful, but it can also kill native species and undermine soil health, with the added threat of harm to humans.

  One frequently used method of control, known as biological control, or “biocontrol,” pits an invasive species’ own enemies against it. In an early success, the cactus moth was introduced to Australia from South America in 1926 to feed on the prickly pear. This plant had itself been introduced in the 1770s and was choking farmland in New South Wales and Queensland. By the early 1930s, most prickly pears had been eradicated.

  Not all biological controls are effective, and some measures have had disastrous consequences. For example, in 1935 cane toads were introduced to Australia to control the invasive grayback cane beetle, which was destroying sugar cane fields. The cane toad had been effective in controlling beetles in Hawaii, so the assumption was that it would be equally successful in Australia. However, grayback cane beetles feed primarily at the top of sugar cane stalks, which is out of reach for the cane toads. A lack of understanding of the different environments favored by the two creatures meant that the cane toad was the wrong choice as a biological control. By the time the mistake was realized, the toad had spread throughout Australia, poisoning any predator species that tried to eat the toxic amphibian.

  Even when biological controls curb an invasive species, they may create imbalances in ecosystems or the economy of local communities. Regulators are, therefore, often hesitant to support biological controls without extensive prior research. No magic bullet exists that can control every invasive species. They are dependent on complex ecosystem interactions, and scientists continue to design field experiments to test their hypotheses of how invasive species function in the wild.

  Since their introduction to Australia in 1935, cane toads have out-competed native frogs because they reproduce far more quickly.

  “Now is the time to take action. The costs to habitats and the economy are … out of control.”

  Bruce Babbitt

  US Secretary of the Interior, (1993–2001)

  The zebra mussel

  The case of the zebra mussel demonstrates the diverse ways to approach invasive species control, and the challenges that result. Zebra mussels are small, fingernail-sized mollusks with a dark-striped shell. The mussel is native to Eurasia but was discovered in the Great Lakes area of North America in 1988, probably carried there in ballast water discharged from ships traveling from Europe. Since then, zebra mussels have spread throughout the midwestern United States, and have been found as far west as California.

  The zebra mussels attach themselves to clams and other mussels, filtering out algae that the native species need for food to survive. They also clog water intake pipes used for power plants and drinking water supplies. Current control mechanisms include chemicals, hot water, and filtering systems. While each has had some success, none of these solutions has been capable of safely eradicating the mussels. As a result, they continue to spread throughout the waterways of the US.

  See also: Predator–prey equations • Nonconsumptive effects of predators on their prey • Human activity and biodiversity • The food chain • The ecosystem • Chaotic population change

  IN CONTEXT

  KEY FIGURE

  Camille Parmesan (1961–)

  BEFORE

  1997 A group of American scientists publishes evidence of a longer plant growing season at northern high latitudes in 1981–91.

  2002 Naturalist Richard Fitter reveals that the first flowering date of 385 plant species in the UK has advanced by 4.5 days in the previous decade.

  AFTER

  2006 Jonathan Banks, from the American Clean Air Task Force, is the first person to use the term “season creep” to describe the increasingly early onset of the seasons as a result of climate change.

  2014 In the US, the National Climate Assessment confirms long-term trends toward shorter, milder winters and earlier spring thaws.

  Most scientists now agree that climate change, driven by an increase in greenhouse gases, is raising the global mean temperature. The Intergovernmental Panel on Climate Change (IPCC) cites an increase of 1.8°F (1°C) since 1880, although in some regions the warming has been even more marked. This warming has affected both plant and animal behavior, and the IPCC forecasts a further increase of 2.5–9.9 °F (1.4–5.5°C) during the next 100 years.

  The life cycles of plants and animals change in line with the seasons. Phenology is the study of these seasonal changes. They may be triggered by temperature, rainfall, or the length of daylight, but temperature is probably the single most important factor in Earth’s temperate and polar regions, whereas rainfall is the key factor in the tropics. In 2003, climate change scientists Camille Parmesan and Gary Yohe proved that spring change is now happening earlier—a phenomenon called spring creep.

  Season creep

  For several decades, people have observed leaves and flowers appearing earlier in spring. In the past, these claims were often dismissed as lacking “hard science,” such as facts, figures, or datasets. When Camille Parmesan and Gary Yohe published evidence in 2003—based on an analysis of more than 1,700 species—they demonstrated that change was very real. Their data showed that spring change was indeed taking place earlier—by an average of 2.3 days per decade. Studies by other scientists in recent years have supported their findings.

  Many of the changes that take place in plants are governed by temperature, including growth spurts; the appearance of leaves, flowers, and fruit; and leaves dying in fall. Most food chains start with plants, so these changes affect grazers and browsers, from rabbits to deer, and pollinators, including bees and butterflies. All of these are at the bottom of the food chain (primary consumers). If they struggle to find food, those that prey on them (secondary consumers) also suffer from the absence of prey.

  All life forms respond to changes in weather brought about by the seasonal cycle. Migration, breeding, flowering, hibernation, and metamorphosis are some of the events affected by this cycle.

  “We are seeing change happen much faster than I thought it would 10 years ago.”

  Camille Parmesan

  Effects of climate change

  A warmer Earth produces many effects. In most cooler parts of the world, the frost-free season is longer than before, providing a longer growing season for plants. As some regions bec
ome drier and some wetter, bouts of extremely heavy rainfall and flooding have become more common. Toxic algal blooms in lakes are occurring more frequently. Ice cover in polar regions is also decreasing. All these changes have affected and will continue to affect animal and plant behavior.

  Since 1993, the European Environmental Agency (EEA) has worked in earnest to pull together data from thousands of studies—dating back to at least 1943—to create a picture of spring creep in Europe. The EEA’s evidence shows earlier dates for plants producing pollen, frogs spawning, and birds nesting. According to their data, many insects whose life cycles are governed by air temperature (thermophilic insects, such as butterflies and bark beetles) now have a longer breeding season, enabling them to produce extra generations each year. For example, some butterflies that previously had two generations now have three.

  In Spain, botanists studied data for 29 species of plants. They found that in 2003, leaves first appeared 4.8 days earlier on average than in 1943; flowers first bloomed 5.9 days earlier; trees produced fruit 3.2 days earlier; and leaves died 1.2 days later. In the UK, the evidence was even more dramatic: across 53 plant species, leaves, flowers, and fruits appeared almost six days earlier in 2005 than they had done in 1976. Similarly, the fruiting season of 315 different kinds of fungi studied in Britain lengthened from 33 to 75 days in the second half of the 20th century.