Bacteria, Viruses and Protistans

1. 
   Characteristics of chordates
   

1. 
   Consists of mostly vertebrates, with a few invertebrate chordates
   

2. 
   Four distinctive features, at some time in their lives
   
   1. 
      Notochord – long rod that supports the body; changes to bone in vertebrates
      
   2. 
      Dorsal, hollow nerve cord
      
   3. 
      Muscular pharynx with gill slits
      
   4. 
      Post-anal tail
      

3. 
   Classified in three subphyla and eight classes (one of which is extinct)
   

2. 
   Invertebrate chordates (Fig. 21.3)
   

1. 
   Tunicates (sea squirts) – 2,000 species
   
   1. 
      Marine organisms covered with a gelatinous tunic
      
   2. 
      Larva resembles a tadpole
      
   3. 
      Adult is sessile and a filter feeder – only gill pouches persist
      

2. 
   Lancelets – 25 species
   
   1. 
      Small fishlike animals
      
   2. 
      Lie buried in sand and filter feed
      
   3. 
      Display all four chordate characteristics throughout their lives
      

3. 
   Jawless fishes
   

1. 
   Earliest were the ostracoderms
   
   1. 
      Covered with hardened external plates
      
   2. 
      Lived on the ocean bottom and were filter feeders
      

2. 
   Existing jawless fishes – lampreys and hagfishes (Fig. 21.7)
   
   1. 
      Have eel-like bodies (but no paired fins) with a cartilaginous skeleton, and two-chambered heart
      
   2. 
      Lampreys are parasitic on other fish; hagfishes are scavengers
      

4. 
   Jawed fishes
   

1. 
   Earliest were the placoderms – now extinct
   

2. 
   Cartilaginous fishes – 850 species (Fig. 21.8)
   
   1. 
      Have a streamlined body with a cartilaginous skeleton, gill slits, paired fins, and two-chambered heart
      
   2. 
      Includes sharks, skates, rays, and chimaeras
      
      1. 
         Sharks are predators with powerful jaws and replaceable teeth (but, some are filter feeders)
         
      2. 
         Skates and rays live on the ocean bottom and feed on invertebrates – some are electric or can sting
         
      3. 
         Chimaeras resemble a rat
         

3. 
   Bony fishes – 20,000 species (Figs. 21.9 & 21.10)
   
   1. 
      Most numerous and diverse of the vertebrates
      
   2. 
      Have a streamlined body (exclu. sea horse) with a bony skeleton, gill flaps, paired fins, two-chambered heart, and swim bladder; most have scales
      
   3. 
      Lobe-finned fishes bear fleshy extensions – coelacanth and lung fishes
      
   4. 
      Ray-finned fishes – modern fish
      

5. 
   Amphibians (Fig. 21.12)
   

1. 
   Evolved from lobed-finned fishes
   

2. 
   Land life represented new challenges
   
   1. 
      Water availability was not reliable
      
   2. 
      Air temperature was variable; air was not the supporting medium that water was, but was a richer source of oxygen
      
   3. 
      New habitats made better sense organs necessary; lots of insects for food
      
3. 
   General characteristics
   
   1. 
      Bony skeletons, usually four legs, and a three-chambered heart
      
   2. 
      Respiration by gills, or by lungs and moist skin (skin supplied with poisonous glands in toads)
      
   3. 
      Most shed their eggs into water, and have a “tadpole” larva
      

4. 
   Includes salamanders (have tails), frogs and toads – 3,000+ species, and caecilians (“worm-like”) – 150 species
   

6. 
   Reptiles (Fig. 21.13)
   

1. 
   Evolved from amphibians
   

2. 
   General characteristics
   
   1. 
      Bony skeletons, four legs, and a three-chambered heart (four-chambered in crocodilians, and possibly dinosaurs)
      
   2. 
      Scaly skin that resists drying; kidneys are good at conserving water
      
   3. 
      Have a copulatory organ that permits internal fertilization; produce shelled eggs which can be laid in dry habitats
      

3. 
   Includes crocodilians, turtles, tuataras, and lizards and snakes
   
   1. 
      Crocodilians – crocodiles and alligators
      
      1. 
         Live in or near water; parents guard nests and assist hatchlings into water
         
      2. 
         Long snouts; body temperature is regulated behaviorally (“sunning”)
         
   2. 
      Turtles – shell for protection (150 species)
      
   3. 
      Tuataras – resemble lizards, but more ancient; only two species, on islands near New Zealand
      
   4. 
      Lizards and snakes
      
      1. 
         Lizards – small bodied insect eaters; live mostly in deserts or tropical forests (3,750 species)
         
      2. 
         Snakes – limbless; excellent predators (poisonous or non-poisonous) (2,300 species)
         

7. 
   Birds – 9,000 species (Figs. 21.14 & 21.15)
   

1. 
   Evolved from small dinosaurs during the Jurassic
   
   1. 
      Oldest known bird – Archaeopteryx
      
   2. 
      Reptilian features of birds – horny beaks, scaly legs, and egg-laying
      

2. 
   General characteristics
   
   1. 
      Body covered with feathers (contour feathers for flight, down feathers for insulation)
      
   2. 
      Constructed for flight – low weight and high power
      
      1. 
         Hollow lightweight bones; powerful muscles for maximum leverage
         
      2. 
         Four-chambered heart and unique lung design
         

8. 
   Mammals – 4,500 species (Fig. 21.17)
   

1. 
   Evolved from small dinosaurs during the Carboniferous
   

2. 
   General characteristics
   
   1. 
      Hair covers at least part of the body (except in whales); milk-secreting glands nourish the young
      
   2. 
      Increased brain capacity, allowing for memory, learning, and conscious tought
      
   3. 
      Teeth (incisors, canines, premolars, and molars) specialized to meet dietary habits
      

3. 
   Reproduction
   
   1. 
      Egg-laying mammals
      
      1. 
         Platypus and spiny anteater (Australia)
         
      2. 
         Modified sweat glands for milk
         
   2. 
      Pouched mammals – marsupials
      
      1. 
         The young are born tiny, blind, and hairless; finish their development in mother’s pouch
         
      2. 
         Most are in Australia, but opossum thrives in North America
         
   3. 
      Placental mammals
      
      1. 
         The young are nourished within mother’s uterus by the placenta
         
      2. 
         Major orders <Not in textbook.>
         
         1. 
            Bats – 925 species
            
         2. 
            Rodents – 1,760 species (mice, rats, squirrels, beavers, porcupines)
            
         3. 
            Hoofed mammals – 200+ species (horses, goats, zebras, elks, deer, etc.)
            
         4. 
            Rabbits, hairs, pikas – 65 species
            
         5. 
            Carnivores – 270 species (dogs, cats, bears, raccoons, skunks, etc.)
            

a. Population size -- number of individuals making up its gene pool

b. Population density -- number of individuals per unit area (or volume)

c. Population distribution -- general pattern in which population members are dispersed through their habitat

d. Age structure -- relative proportions of individuals of each age (esp. with respect to reproductive years)
2. Population dispersal patterns

a. Clumped -- very common

b. Uniform -- rare, usually the result of fierce competition for limited resources

c. Random -- environmental conditions are uniform and members are neither attracting nor repelling each other

a. Population size dependent on births, immigration, deaths, and emigration

b. Population size increases if there are more births than deaths, and decreases if there are more deaths than births

c. Zero population growth -- balance of births and deaths

a. Growth rate formula -- G = rN

1) r -- net reproduction per individual per unit time

2) N -- number of individuals

b. Results in a J-shaped curve that becomes steeper with time (Fig. 35.2)

c. As long as "r" is positive, population will continue to increase at ever-increasing rates

d. Doubling time -- amount of time to double the population
3. Biotic potential -- maximum rate of increase under ideal (nonlimiting) conditions
D. Limits on growth of populations
1. Limiting factors

a. Actual rate of increase of a population is influenced by environmental conditions

b. Limiting factors (nutrient supply, predation, competition for space, pollution, metabolic wastes) provide environmental resistance to population growth
2. Carrying capacity and logistic growth

a. Carrying capacity -- defined by the sustainable supply of resources for a particular population in a given environment

b. Logistic growth -- S-shaped curve caused by the carrying capacity varying over time
3. Density-dependent controls

a. Main density-dependent factors -- competition for resources, predation, parasitism, disease, etc.

b. These factors exert their effects in proportion to the number of individuals present
4. Density-independent controls

a. Tend to increase the death rate without respect to the number of individuals present

b. Ex. -- weather (lightning, floods, snowstorms, etc.)
E. Life history patterns
1. Life tables -- follow the fate of a groups of newborn individuals (cohort) through their lives to calculate survivorship schedules
2. Survivorship curves -- plots of age-specific patterns of death for a given population in a given environment (Fig. 35.5)

a. Type I curve -- typical of large mammals, where infant mortality is low; death usually comes after an extended life

b. Type II curve -- chances of survival or death are about the same at any age

c. Type III curve -- low survivorship or high mortality in early life

1. 
   Factors that shape community structure
   

1. 
   Community – association of interacting populations of different species living in a particular habitat
   
   1. 
      Habitat – place where an organism lives; characterized by distinctive physical features and vegetation
      
      1. 
         Interactions between climate and topography dictate rainfall, temperature, soil composition, etc.
         
      2. 
         Availability of food and resources affects inhabitants
         
      3. 
         Adaptive traits enable individuals to exploit specific resources
         
      4. 
         Interactions of various kinds (competition, predation, mutualism) occur among the inhabitants
         
      5. 
         Physical disturbances, immigration, and episodes of extinction affect the habitat
         
   2. 
      Several community properties result from factors above
      
      1. 
         Species are found at different feeding levels from producers to consumers
         
      2. 
         Diversity increases in tropical climates, creating species richness
         

2. 
   Niche – the “occupation” of a species
   
   1. 
      Defined by the full range of physical and biological conditions under which the individual lives and reproduces
      
   2. 
      Each species has its own niche defined, in part, by its relationships with other organisms
      

3. 
   Categories of species interactions
   
   1. 
      Interactions can occur between any two species in a community and between entire communities
      
   2. 
      Several types of species interactions
      
      1. 
         Neutral – neither species directly affects the other (ex., eagles and grass)
         
      2. 
         Commensalism – one species benefits and the other is not affected (ex., bird’s nest in tree)
         
      3. 
         Mutualism – both species benefit (ex., lichens, yucca plant and yucca moth)
         
      4. 
         Interspecific competition – both species are harmed
         
      5. 
         Predation and parasitism – one species benefits while the other is harmed
         

2. 
   Competitive interactions
   

1. 
   Categories of competition
   
   1. 
      Intraspecific – competition within a population of the same species; may result in depletion of a resource
      
   2. 
      Interspecific – competition between species; less intense because requirements are less similar
      
   3. 
      Two types, regardless of whether they are intra- or interspecific
      
      1. 
         Exploitation competition – all individuals have equal access to a resource, but differ in their ability (speed or efficiency) to exploit that resource
         
      2. 
         Interference competition – some individuals limit others’ access to the resource
         

2. 
   Competitive exclusion – two species require the same resource
   
   1. 
      Suggests that complete competitors cannot coexist indefinitely; differences in adaptive traits give certain species the competitive advantage
      
   2. 
      When competitors’ niches do not overlap as much, coexistence is more probable
      

3. 
   Resource partitioning
   
   1. 
      Similar species share the same resources in different ways
      
   2. 
      Resource partitioning arises in two ways
      
      1. 
         Ecological differences between established and competing populations may increase through natural selection
         
      2. 
         Only species that are dissimilar from established ones can succeed in joining an existing community
         

3. 
   Predation and parasitism
   

1. 
   Predator vs. parasite
   
   1. 
      Predators – get their food from prey, but do not take up residence on or in the prey
      
   2. 
      Parasites – get their food from hosts, and live on or in the host for a good part of their life cycle
      

2. 
   Dynamics of predator-prey interactions
   
   1. 
      The dynamics, ranging from stable coexistence to recurring cycles, depend on:
      
      1. 
         Carrying capacity of prey population in the absence of predation
         
      2. 
         Reproductive rates of prey and predator
         
      3. 
         Behavioral capacity of individual predators to respond to prey density