(44) Climate Science

Examples of Terrestrial Animals

What are terrestrial organisms? What are some examples of them?

Terrestrial Organisms



Climate Models

Terrestrial organisms

Warmer temperatures have increased growing seasons, with spring arriving earlier and fall coming later for many species of land plants and animals. The second half of the twentieth century saw an increase in growing season of up to two weeks in the mid and high latitudes, with many more frost-free days. The length of a growing season at a single research station in Spain increased by 32 days between 1952 and 2000, and the average increase across Europe was from 1.1 to 4.9 days per decade. Longer growing seasons and warmer temperatures are sometimes accompanied by higher productivity, range changes, and earlier spring and summer seasonal events.

The total effect of growing season length on productivity is unclear. Satellite data show that a lengthened growing season caused increased productivity in the Northern Hemisphere from 1982 to 1991. However, from 1991 to 2002, productivity decreased there, possibly due to hotter, drier summers and more widespread droughts.

Coral Reefs

Coral reefs are known as the “rain forests of the sea” because they harbor such an incredible abundance and diversity of life. These spectacular and beautiful ecosystems are home to more than one-fourth of all marine plant and animal species. Reefs are built of tiny coral animals called polyps that construct calcium carbonate (CaCO3) shells around their bodies. When the larva from a young coral polyp attaches itself to a good spot, usually on an existing coral, and builds a shell, the reef grows. The coral polyps enjoy a mutually beneficial relationship with minute algae called zooxanthellae. In this relationship, the photosynthetic algae supply oxygen and food to the corals, and the corals provide a home and nutrients (their wastes) for the zooxanthellae. The algae give the coral their bright colors of pink, yellow, blue, purple, and green. Coral polyps sometimes feed by capturing and eating the plankton that drift into their tentacles.

Corals can thrive only in a narrow set of conditions. They are very temperature sensitive, so the water must be warm, but not too hot. Water depth must be fairly shallow, with moderately high but constant salinity. The zooxanthellae must have clear, well-­ lit water to photosynthesize. Coral reefs protect shorelines from erosion and provide breeding, feeding, and nursery areas for commercially valuable fish and shellfish.

Damaged coral reefs sometimes turn white, a phenomenon called coral bleaching. First recognized in 1983, coral bleaching has become quite common. When coral animals are stressed, they expel their zooxanthellae. Since these algae give the coral its color, only the white limestone is left when they are gone. Sometimes zooxanthellae move back in when conditions improve, but if they are gone for too long, the corals starve and the reef dies. Coral reefs may recover from one bleaching event, but multiple events can kill them. Disease in corals and some other reef organisms has increased, especially in reefs that are already stressed.

Dr. Clive Wilkinson, coordinator of the Global Coral Reef Monitoring Network, blames the current upsurge in coral bleaching on rising seawater temperatures due to global warming. An increase in summer maximum temperatures of 1.8°F (1°C) for two to three days can trigger a coral bleaching event. If the elevated temperatures persist for less than one month, the reef will likely recover, but sustained heat will cause irreversible damage. After some high temperature episodes, the resident zooxanthellae have been replaced by a more heat tolerant species, and so the reef survives. However, many reefs are already found in the warmest water that zooxanthellae can tolerate, so this process is unlikely to save many reefs in the According to Wilkinson’s report, Status of Coral Reefs of the World: 2004, 20% of coral reefs are severely damaged and unlikely to recover, and another 24% are at imminent risk of collapse.

A wide variety of plants and animals have undergone recent range changes due to rising temperatures. An analysis of more than 1,700 species by Camille Parmesan of the University of Texas, Austin, and Gary Yohe of the University of Middletown, Connecticut, published in Nature in 2003, concluded that there has been a northward range shift of 3.8 miles (6.1 km) per decade. In tundra communities, a shift toward the poles or up mountains may result in a small decrease in range or replacement by trees and small shrubs. North American animals with ranges that are shifting northward include pikas (Ochotona sp.), Rufous hummingbirds (Selasphorus rufus), sea stars (of the class Asteroidea), and red foxes (Vulpes vulpes). Species of plants and animals that have never before been seen in the Arctic are moving in, such as mosquitoes and the American robin (Turdus migratorius). Antarctic plants have increased in abundance and range in the past few decades. Species are disappearing in the lower latitude portions of their ranges. In North America, the Edith’s checker spot butterfly (Euphydryas editha) is almost extinct in Mexico but thriving in Canada. Adélie penguins are now thriving at their southernmost locations but have experienced large population declines where they are found farthest north on the Antarctic Peninsula.

Organisms are also moving up in altitude. Besides contracting in the southern end of their range, many more populations of Edith’s checkers pot butterfly are becoming extinct in the lower elevation portions of their range (40%) than in the highest portions of their range (less than 15%). As a result, the mean elevation of the butterfly has moved upwards by 344 feet (105 m). In the Great Basin of the United States, the lower elevation populations of pika (Ochotona princeps) that were documented in the 1930s were extinct by the early 2000s because the animals have been found to die when the temperature reaches 88°F (31°C) for more than one half hour. In the Alps, native plant species have been driven off mountaintops as they search for favorable conditions and as nonnative plant species move uphill. Migrating animals are changing their ranges. Increasing numbers of European blackcap warblers (Syliva atricapilla) that have traditionally wintered in Africa are now migrating west to Great Britain. Chiffchaffs (Phylloscopus collybita) no longer migrate south, but remain in the United Kingdom for the winter. Of the 57 species of European butterflies Parmesan studied, the ranges of 35 of them were migrating northward: For example, the Apollo (Parnassius apollo), moved 125 miles in 20 years. The Purple Emperor (Apatura iris), unknown in Sweden until the early 1990s, has been increasing its population there. African species, such as the Plain Tiger (Danaus chrysippus), have moved into Spain.

In some species, life cycle events that are tied to day length or temperature are now occurring at different times. The springtime emergence of insects, egg laying in birds, and mating in all animal types is events that have advanced to earlier in the spring. Parmesan and Yoye detected an advancement of spring events of 2.3 days per decade averaged for all species and 5.1 days per decade averaged only for species that showed a change. These changes have been seen in plants, such as lupines (Lupinus sp.); insects, such as crickets and aphids; amphibians; and birds. For example, frogs in eastern North America and in England have been found to breed weeks earlier than they did early in the twentieth century. In mammals, high latitude and altitude species show the most changes. For example, yellow-bellied marmots (Marmota flaviventris) in the Rocky Mountains emerged from their winter hibernation 23 days earlier from 1975 to 1999.

Phenology is relatively easy to study in birds because the animals are visible, and their life cycles are highly regulated by seasonal changes. In many species, temperatures and conditions on the wintering grounds determine spring migration dates. British observers have noted that migratory birds now arrive in their breeding grounds 2 to 3 weeks earlier than they did 30 years ago. The egg laying dates of these birds have also advanced-an average of 8.8 days for 20 species between 1971 and 1995.

In some European flycatchers, the egg laying dates match trends in local temperature. For each 3.6°F (2°C) rise in temperature, the birds lay their eggs two days earlier. Unfortunately, the life cycles of the plants and invertebrates that these birds rely on for food have advanced even more, by about six days for each 3.6°F (2°C) rise in temperature. This timing discrepancy may, at some point, cause problems for the birds because their young will hatch well after their food sources peak. Already in some species, such as pied flycatchers (Ficedula hypoleuca), the number of young birds that hatch each year is smaller.

In some vulnerable locations, changing temperatures have led to the loss of suitable habitats, which is having a dramatic impact on some species. (A habitat is the natural environment of an organism, including the climate, resource availability, feeding interactions, and other features.) The loss of arctic sea ice, for example, is destroying the habitat that is needed by polar bears and northern seals. In the southern edge of their range, where ice is melting and hunting time is reduced, polar bear populations are in significant declines, and their mean body weight is decreasing. In addition, warmer temperatures have caused the populations of ringed seals, the bears’ main food, to decline. In the northern portions of their range, significant numbers of polar bears have drowned because they are unable to swim the greater distances between ice floes. These more northerly polar bears are also experiencing lower reproductive success and lower body weight. The direct effects of temperature changes affect animals differently. Populations of some birds increase when temperatures are high. But, as scientists have learned from El Niño events, when eastern Pacific Ocean temperatures are high, whales have less reproductive success. Some species experience mixed effects: Emperor penguins have greater hatching success when water temperatures rise, but the birds must swim farther from shore to feed, which puts a great strain on them. Also, the instability of ice shelves has reduced nesting success. These competing forces have resulted in a 70% decrease in emperor penguin populations since the 1960s.

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