CK-12 Life Science
Page 34
What are some other economic uses of birds? One is the harvesting of guano (droppings) for use as fertilizer. Another is the use of chickens as an early warning system of diseases, such as West Nile Virus, that affect humans. In the latter example, mosquitoes carry the West Nile Virus, bite young chickens and other birds, and infect them with the virus. The first human cases of the virus usually follow the first appearance of infected birds within three months. Blood samples from young chickens can be tested for the presence of antibodies to the virus, and if detected, then this is an early warning that human infection can follow.
What about how birds can be important ecologically? For example, some nectar-feeding birds are important pollinators, and many frugivores, or fruit-eating birds, help disperse seeds. Birds are often important to island ecology, since they can easily reach islands. In New Zealand, the Kereru and Kokako are important browsers (animals that eat or nibble on leaves, tender young shoots, or other vegetation) and seabirds enrich the soil and water with their production of guano (Figures below and below).
Figure 14.9
The Kereru is an important browser species in New Zealand.
Figure 14.10
The Kokako, another important browser species of New Zealand.
Finally, let’s not forget that birds have had a relationship with humans since the dawn of humanity. Sometimes, as in the cooperative honey-gathering among honeyguides and African peoples such as the Borana, these relationships are mutualistic, where both benefit. Birds also play prominent and diverse roles in folklore, religion, and popular culture, and have been featured in art since prehistoric times, as in early cave paintings. Perhaps their beauty and diversity will always capture the imagination of humans.
Lesson Summary
Most of birds’ traits are related to their being warm-blooded or their adaptations for flight.
Adaptations for flight involve features that are lightweight, flexible, strong and that take advantage of air currents.
The components of reproduction usually involve a courtship display, nest production, egg-laying, incubation and parental care. There is much diversity demonstrated in adaptations for predator avoidance.
With 10,000 bird species there is a lot of diversity. Specialized structures are adapted for specific habitats or living requirements.
Birds are important economically, ecologically and in human culture.
Review Questions
List five traits which are important for flight.
Describe how a bird’s breeding system can be adapted to avoid predation.
Explain how the absence of land predators on islands would result in flightlessness in birds.
You detect the presence of antibodies to the West Nile Virus in young chickens. How did the chickens get the virus? When would the first human cases of the virus most likely occur?
Further Reading / Supplemental Links
Department of Health, Florida. Available on the web at: www.doh.state.fl.us.
Oliver L. Austin, Birds of the World. Western Publishing Company, Inc., New York, 1961.
Unabridged Dictionary, Second Edition. Random House, New York, 1998.
http://en.wikipedia.org/wiki/West_Nile_virus
http://www.birds.cornell.edu/AllAboutBirds/studying
http://kids.nationalgeographic.com/Animals
http://www.ucmp.berkeley.edu/diapsids/birds/birdintro.html
http://www.personal.psu.edu/users/h/j/hjs130/aves.html
http://www.fs.fed.us/global/wings/birds.htm
Vocabulary
aerofoil
A surface which is designed to aid in lifting or controlling by making use of the air currents through which it moves.
altricial
A reproductive system in birds in which the newly hatched young are small, naked, immobile and blind.
monogamous
A mating system in birds where the couple pair for the duration of the breeding season or sometimes for a few years or until one mate dies.
polygamous
A mating system in birds where there is more than one mate.
precocial
A reproductive system in birds in which the newly hatched young are feathered and mobile.
Points to Consider
Birds and mammals are the only warm-blooded vertebrates. As in birds, mammals exhibit wide diversity and live in varied habitats. Based on what you know about adaptations in birds, how do you think mammalian limbs are adapted for locomotion in different habitats?
As in birds, mammals also have specialized diets. Instead of beaks, mammals have different kinds of teeth. In what way(s) do you think teeth in mammals are adapted for different kinds of diets?
Lesson 14.2: Mammals
Lesson Objectives
List and describe general traits of mammals.
Compare reproduction in monotremes, marsupials and placental mammals.
Describe how mammals can be grouped according to their anatomy and their habitats.
Explain how non-human mammals can benefit people and how they play an ecological role.
Check Your Understanding
What traits are there in mammals as a result of their being warm-blooded?
Answer: They have fur to decrease heat loss; their diets contain high energy foods, and methods of feeding help to maintain a high metabolism; and, they conserve energy both by being inactive at certain times of day and in some cases, by hibernation.
Describe courtship displays in birds. As you learn about mammals, think about how their courtship is similar to, or differs from that seen in birds.
Answer: Males usually perform courtship displays in birds. Most displays involve a type of song and some displays are very elaborate and may include dancing, aerial flights, or wing or tail drumming.
Introduction
What is a mammal? It is easy to forget about the biodiversity of mammals, but these animals range from bats and cats and rats to dogs and monkeys and whales. They walk and run and swim and fly. They live in the ocean, they fly in the sky, they walk on the prairies and run in the savannah. What allows them to live in such diverse environments? They have some specialized traits which no other group of animals has. There is a tremendous amount of diversity within the group in terms of reproduction, habitat, and adaptation for living in those different habitats. Some of their traits directly benefit people, while also playing an important ecological role.
Characteristics of Mammals
Mammals (class Mammalia) are warm-blooded, vertebrate animals with a number of unique characteristics. In most mammals, these include:
The presence of hair
Sweat glands
Glands specialized to produce milk (mammary glands)
Three middle ear bones
A neocortex region in the brain
Specialized teeth
A four-chambered heart
All mammals, except for the monotremes (the most primitive order of mammals, with certain birdlike and reptilian characteristics, such as laying eggs, and a single opening for the urinary, genital, and digestive organs), produce live young (known as vivipary) instead of laying eggs.
There are approximately 5,400 mammalian species, ranging in size from the tiny 1-2 in (30-40mm) bumblebee bat to the 1,083ft (330m) blue whale. These are distributed in about 1,200 genera, 153 families and 29 orders. (see http://users.tamuk.edu/kfjab02/Biology/mammalogy/mammal_classification.htm).
Reproduction in Mammals
Keep in mind what you have learned about reptiles and birds and see how mammals might be both similar and different to these groups. The egg-laying monotremes, such as echidnas (Figure below) and platypuses (Figure below), use one opening, the cloacae, to urinate, defecate and reproduce, just as lizards and birds do. They lay leathery eggs, similar to those of lizards, turtles and crocodilians. Monotremes feed their young by “sweating” milk from patches on their bellies, since they lack the nipples present on other mammals.
Figure 14.11
The echidna is a member of the monotremes, the most primitive order of mammals.
Figure 14.12
Another monotreme, the platypus, like other mammals in this order, lays eggs and has a single opening for the urinary, genital, and digestive organs.
All other mammals give birth to live young and are either marsupial or placental. The females of most marsupials have an abdominal pouch or skin fold within which are mammary glands and a place for raising the young (Figure below). Placental mammals have a placenta that nourishes the fetus and removes waste products.
Figure 14.13
A marsupial mammal, this Eastern grey kangaroo has a joey (young kangaroo) in its abdominal pouch.
Some mammals are solitary except for brief periods when the female comes into estrus, the optimal time for a female to become pregnant. Others form social groups where a differences between sexes (sexual dimorphism) is frequently extreme. Dominant males are those that are largest or best-armed. These males usually have an advantage in mating or may exclude other males from access to females within a group, such as seen in elephant seals (Figure below). This group of females forms a harem. Think back to what you learned about courtship displays in birds. How is such conduct in mammals similar or different?
Figure 14.14
A mating system with a harem of many females and one male, as seen in the seal species, .
Groups of Mammals
As is true for most animal groups, mammal groups can be characterized in a number of ways, e. g., according to their anatomy, the habitats in which they live, and/ or their feeding habits.
Most mammals belong to the placental group. Within this group are several subgroups including lagomorphs (hares and rabbits) and rodents (rats, mice and other small, gnawing mammals); carnivores (cats, dogs, bears and other mammals that are primarily meat eaters) (Figure below); insectivores (including moles and shrews) (Figure below); a group including bats and primates; ungulates (hoofed animals, including for instance deer, sheep, goats, pigs, buffalo and elephants), and whales and manatees) (Figure below).
Figure 14.15
A Caracal, hunting in the Serengeti.
Figure 14.16
One of the subgroups of placental mammals is the insectivores, including moles and shrews. Pictured here is the Northern short-tailed shrew.
Figure 14.17
The ungulates (hoofed animals) like the giraffe here, is another of the subgroups belonging to the placental mammals
Why do you think the above groups of animals are placed together? Can you think of some examples of tooth type that are adapted for a mammals’ diet and types of limbs that are adapted for living in different types of habitats?
Mammals can also be grouped according to the habitat they live in and with adaptations for living in that habitat. Terrestrial mammals with saltatory (leaping) locomotion, as in some marsupials and in lagomorphs, is typically found in mammals living in open habitats. Other terrestrial mammals are adapted for running, such as dogs or horses. Still others, such as elephants, hippopotamuses and rhinoceroses, have a cumbersome (and hefty) mode of locomotion known as “graviportal.”
Other mammals are adapted for living in trees (arboreal), such as many New World monkeys (Figure below). Others are fully aquatic, such as manatees, whales, dolphins and seals, and others are adapted for flight, as are bats, or gliding (some marsupials and rodents).
Figure 14.18
This howler monkey shows adaptations for an arboreal existence.
Significance of Mammals
Mammals are thought to be significant both in terms of how they benefit people and also of their importance ecologically. Given what you know about mammals so far, how do you think they may be important to people? Just examining our daily lives we see examples of mammals (other than people!) serving our needs everywhere. We have pets that are mammals, most commonly dogs and cats; if we live in rural areas or visit another country we will probably see lots of examples of mammals used for transport (horses, donkeys, mules and even camels), being raised for food (cows and goats), and used for work (dogs (Figure below), horses, and elephants).
Figure 14.19
A Labrador Retriever working as an assistance dog.
The special capabilities of some mammal species have been used in practical situations and also to increase our knowledge. Can you think of how they have been used? For example, the United State and Russian militaries have trained and employed oceanic dolphins to rescue lost divers or to locate underwater mines. Mammals’ more highly developed brain has made them ideal for use by scientists in studying such things as learning, as seen in maze studies of mice and rats. The ability of young mammals to learn from the experience of their elders has allowed a behavioral plasticity unknown in any other group of organisms and has been a primary reason for the evolutionary success of mammals. See if you can come up with some other examples.
Mammals have also played a significant role in different cultures’ folklore and religion. For example, the grace and power of the cougar have been widely admired in the cultures of the indigenous peoples of the Americas. The Inca city of Cusco is reported to have been designed in the shape of a cougar and the sky and thunder god of the Inca, Viracocha, has been associated with the animal. In North America, mythological descriptions of the cougar have appeared in stories of a number of Native American tribes.
Ecologically, nectar-feeding and fruit-eating bats (Figure below) play an important role in plant pollination and seed dispersal, respectively. Can you think of a type of bird that has a similar ecological role?
Figure 14.20
Bats, like this Egyptian fruit bat, belong to another subgroup of placental mammals. Ecologically, fruit bats play an important role in seed dispersal.
Mammals are also the only animal group that has made a complete transition to aquatic habitats. Some, such as cetaceans (whales, dolphins and porpoises) have undergone profound adaptations for swimming and life, even reproduction, in the water. Cetaceans depend on water for mechanical support and thermal insulation. Because they are buoyed by their aquatic environment, whales have evolved into the largest mammals and the largest animals ever recorded.
Micro-Lab: Matching Adaptations of Teeth and Limbs in Mammals with their respective Diets and Habitats
Estimated time: 15 minutes
Materials:
1. Tray of actual, or illustrations of, various mammal teeth, numbered, and Pictures of animals eating:
Incisors – cutting and nipping (herbivores, like cows, have well-developed incisors for cutting grass)
Premolars – shearing and grinding (herbivores, like cows, have flat premolars and molars for grinding vegetation)
Canines – piercing (carnivores, like lions, have long and strong canines.)
2. Tray of actual, or illustrations of, various mammalian limbs, numbered (for feet, could also show cast of track, to see if students can match the track with the actual foot type) and pictures of habitats or actual animals, lettered:
Toe ending in claws – tiger (climbing and running)
Toes with hooves – horses and cows (running)
Fins – aquatic mammals (swimming)
Wings – bats (flying)
Highly mobile limbs – monkeys (climbing in trees)
3. Answer sheets, listing numbered mammal teeth and limbs
Directions:
One group of students examines the tray of mammal teeth and pictures of diets and indicates on the answer sheet the correct matches. The other group of students examines the tray of mammal limbs and pictures of habitats and similarly matches these up with the correct answers.
Links to websites with pictures of mammal teeth and/or limbs: Teeth:
http://www.vinsweb.org/education/elf/units/tas.html
http://www.teachersdomain.org/resources/tdc02/sci/life/stru/jaws/index.html
Teeth and Limbs:
http://www.acornnaturalists.com/Mammal-Activities-C227.aspx
Lesson Summary
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The class Mammalia is distinguished by the presence of hair, sweat glands, three middle ear bones and a neocortex area in the brain.
There is a lot of variation in mammalian reproductive systems. Mammals consist of both the egg-laying monotremes and those that are viviparous. The latter group includes marsupial and placental mammals. Diversity can also be found in mammalian mating systems.
The 5,400 species of mammals can be grouped according to anatomical features as well as the type of habitat found in. Mammals have specific adaptations for living on land, in trees, in water and for flight.
Non-primate mammals have an important relationship with people as well as fulfilling necessary ecological functions.
Review Questions
What are two ways in which monotremes differ from viviparous mammals?
With respect to characteristics of feet, limbs and tails, what features would you expect mammals to have for jumping?