Ecology 3 Flashcards
What is a stable climax community?
A community that remains the same in its composition and size over a long period of time
What is a climax community?
A maximum community that a given habitat can support
Give examples of climax communities
A mature forest and grassland
What causes a climax community to change?
Some factor in the ecosystem is changed such as the introduction of a new species or a change in climatic conditions
What can destroy a climax community?
Human activities or natural happenings like a volcanic eruption
What does the destruction of a climax community usually result in?
The formation of a new habitat
How are new habitats constantly being formed?
By the weathering of rocks
When else are new habitats formed?
When lakes and ponds fill up and rivers build deltas at their mouths
What happens to a new habitat over a long period of time?
It undergoes changes to form a climax community
What is an important process in a new habitat like a bare rocky area?
Soil formation
What are usually the first organisms to colonize a bare rock?
Lichens They are known as pioneer organisms
What abiotic factors help lichens crumble the rock surface leading to soil formation?
Rain diurnal temperature changes and wind
How long does the process of soil formation take?
Thousands of years
Describe newly formed soil
A harsh habitat exposed to the sun wind and rain It contains very little humus
What organisms colonize newly formed soil?
Hardy grasses and weeds This community is scanty and scattered
What does the pioneer community do to the habitat?
It brings about further changes making conditions more favorable for living organisms
What happens as the habitat changes?
New species establish themselves and their numbers increase
What causes earlier communities to be replaced by later ones?
Changing habitat conditions and competition for resources
What is the result of the process of communities replacing each other?
A stable climax community is formed
What is the likely climax community in a new habitat in a tropical lowland region with ample rainfall?
A rain forest
What is succession?
The step by step orderly and gradual replacement of communities that leads to a climax community
What are the two types of succession?
Primary succession and secondary succession
Where does primary succession occur?
In an area where no community existed before
What does primary succession involve?
The formation of new soil
Where can primary succession begin?
From a bare dry environment or an aquatic environment
Give examples of primary succession
A large rocky slope changing to a forest shallow lakes filling up to become marshes and then forests and mud deposited at river mouths building up into mangrove swamps and eventually rain forests
What is the first stage of succession at river mouths?
Deposition of silt results in the formation of mud banks
What are the characteristics of these new mud banks?
They support very little life since the soil is saturated with salt and submerged during high tide
What are the first plants to colonize new mud banks?
Red mangrove trees with stilt roots and breathing roots
What happens after red mangrove trees colonize the mud banks?
Other mangrove plants colonize the banks and a mangrove swamp is formed
What animals come to feed in the mangrove swamp?
Birds insects crabs snails and slugs
What causes the mud bank to rise higher?
The constant accumulation of mud and plant and animal remains
What plant community replaces the red mangrove community?
A community dominated by white mangrove trees which prefer higher and drier ground
What happens to old mud banks as new ones form further out to sea?
The old mud banks are gradually converted into inland areas
What happens after a long time to the accumulated plant and animal remains?
They raise the land well above high tide level and a more normal soil develops
What replaces the white mangrove community?
A large number of different trees shrubs herbs grasses ferns climbers and epiphytes
What animals colonize this habitat?
Squirrels rats snakes mongooses and monkeys
What contributes to the formation of a normal forest flora and fauna?
The continuous formation of humus
What is the final stable community called?
The climax of the succession
What are the first colonizers of a newly formed pond?
Producer plankton
What happens to the pond water as plant remains and soil wash in?
It becomes shallower
What plants grow in the shallow waters?
Higher plants like pondweeds
What happens as the pond margins fill in?
Reeds sedges and other marsh plants replace the pondweeds which colonize areas nearer the center of the pond
What does the whole pond eventually become?
A dry terrestrial habitat supporting a suitable climax vegetation
When does secondary succession occur?
When an existing community on a terrestrial habitat is disturbed
What may still be present in a disturbed habitat?
Some soil and probably certain organisms
What causes secondary succession to occur?
Fires droughts and floods abandoned farmland overgrazed grassland and cleared forest areas
How does the time frame of secondary succession compare to primary succession?
Primary succession takes thousands of years but secondary succession is much faster
Why is secondary succession faster than primary succession?
Soil which takes a long time to form is already present and plants from the surrounding communities and those that survived can readily revegetate the disturbed area
What does the pioneer community in secondary succession include?
Plants from the previous climax community
What is the general progression of an abandoned farm to a climax community?
Annual weeds → Perennial herbs → Shrubs and trees
What is secondary succession?
The series of changes in the communities that occur in a disturbed terrestrial habitat leading to a climax community
When does overcrowding occur?
When a population in a given habitat increases beyond a point where the resources are not enough to support all the individuals
What will be studied in this section?
The factors that lead to overcrowding the effects of overcrowding and the adaptations practiced to avoid it
How do living organisms exist in a habitat?
Not singly but as populations
What is a population?
The total number of individuals of a given species in a habitat at a given time
What can the individuals in a population consist of?
Males females adults juveniles larvae eggs or seeds
What is population density?
The average number of individuals of a species per unit area of the habitat
How can we find the population density of people in a state?
By counting the people in it and dividing by the area of the state
Give an example of calculating population density
Kano State with a population of 6995000 people and an area of 43 072 square kilometers has a population density of 162 people per square kilometer
Is it usually possible to count all individuals in a habitat?
No
How is population estimated?
By sampling techniques
Does a population grow indefinitely in nature?
No
What keeps the population density of a species in check?
Environmental factors
What happens to the population size of mice when introduced into a new habitat with abundant food and favorable growth conditions?
At first it increases slowly then undergoes exponential growth (doubling at regular intervals) slows down and eventually ceases to grow
Why does the population of mice eventually stop growing?
Because certain factors limit further increase in population size
What is the steady population size that a habitat can support called?
The carrying capacity of the habitat
What is the typical growth pattern of a population when food is abundant and growth factors are not limiting?
An S-shaped sigmoid curve
What factors cause the density of a population to increase or decrease?
Natality mortality immigration and emigration
How does natality affect population density?
It increases it by adding new individuals
How does mortality affect population density?
It decreases it by removing individuals
How does immigration affect population density?
It increases it as individuals move permanently into the area
How does emigration affect population density?
It decreases it as individuals move out permanently
What causes overcrowding?
Population increase beyond the carrying capacity of a habitat because resources like food and space are insufficient
Does each species in an ecosystem have its own ecological niche?
Yes feeding on specific food and living in a particular part of the microhabitat
How does the specificity of needs affect population size?
Species with very specific needs have small populations while those with less specific needs have large populations
What two factors add individuals to a population and lead to overcrowding?
Natality and immigration
Which of these factors causes a population to increase in size rapidly?
High natality
When is natality generally high?
In a population with a large number of individuals in the reproductive age group (a young population)
What other factor increases birth rate in species with separate sexes?
A large number of females with a high fertility rate
What type of age-sex population pyramid indicates a population that can increase rapidly in size?
A broad-based pyramid
What other factor causes an increase in population size?
a high survival rate
In what animals is a high survival rate found?
Animals like rabbits mice and humans
Why do these animals have a high survival rate?
They look after their young and protect them from predators
What does a high survival rate enable individuals to do?
Reach sexual maturity and reproduce before they die
What are the characteristics of this type of population?
high life expectancy and low mortality among the young with a sharp rise in mortality in old age
What kind of population is capable of increasing in size rapidly and overshooting the carrying capacity of its habitat?
A young population with a high natality rate and high survival rate
What limits further increase in population size when overcrowding occurs?
Environmental factors which create an environmental resistance to population growth
List some of the important factors that check population growth
Food shortage shortage of other resources restricted living space diseases competition predation and build-up of toxic wastes
What did laboratory studies on rats show about overcrowding?
It induces physiological and hormonal changes causing aggressive behavior low birth rate and eating of young
What do the limiting factors of overcrowding do?
Increase deaths and emigration and decrease reproductive rates
How do plants avoid overcrowding?
By the dispersal of their seeds and fruits by agents like animals wind and water
Give examples of plant adaptations for seed dispersal
Edible fruits eaten by birds with seeds passing through their digestive tract sticky or hooked seeds clinging to animal fur and light or winged seeds and fruits carried by the wind
What are the advantages of seed dispersal?
It prevents overcrowding and allows the plant species to colonize other suitable habitats
How do many animals avoid overcrowding?
By migration - large scale seasonal movements between habitats
What environmental factor causes migration in the savanna?
Seasonal changes affecting food supply
What happens to the carrying capacity of the savanna habitat?
It fluctuates being high during the rainy season and low during the dry season
When does overcrowding occur in the savanna?
During the dry season when food becomes scarce
What do animals do to overcome seasonal food shortages?
They move to other habitats during the unfavorable season and return when it becomes favorable
What are some limiting factors that cause migrations?
Seasonal food shortages cold winter temperatures and breeding
Describe the migration of the white stork
It nests in Europe during the summer and migrates to West Africa and eastern and south-eastern Africa in autumn
Give examples of local bird migrations in the savanna
Southward movement of some savanna birds like the kite and the village weaver to the forest zone during the dry season
Describe migrations of large African mammals in the savanna
They migrate with the dry and wet seasons For example wildebeests of the Serengeti plains travel more than 2000 kilometers
Is the swarming of desert locusts considered migration?
No it is a one way journey
What causes desert locusts to swarm?
Food shortage causes them to crowd into areas with green vegetation
What does overcrowding cause desert locusts to do?
Undergo hormonal changes and produce large numbers of migratory locusts which differ in color structure behavior and physiology
What happens when migratory locusts swarm?
They invade vegetated regions and strip them bare of foliage Swarms can consist of up to 10000 million individuals
Why do birds need to be migratory?
Because they need to eat a lot of food frequently due to their high metabolic rate and an abundant food supply is seldom present throughout the year in most habitats
What adaptation do birds have for migration?
They are adapted to travel long distances without wasting energy
How do some species avoid overcrowding?
By having life cycles where the young and adults occupy different ecological niches
Give examples of species that avoid overcrowding by having young and adults in different ecological niches
Toads (tadpoles in water adults on land) caterpillars and butterflies (caterpillars eat leaves adults eat nectar)
How else is overcrowding prevented?
By having life spans where adults usually die shortly after producing young
What is territorial behavior?
A behavior where individuals usually males mark out areas or territories for living and breeding and defend them against others of the same species
What are the benefits of territorial behavior?
The most vigorous individuals establish large territories and get a large supply of resources attract mates and produce many offspring passing on their favorable traits
What are the effects of territorial behavior on the population?
Individuals are spaced out preventing overcrowding
Give examples of animals that exhibit territorial behavior
Rainbow lizard (Agama agama) male fiddler crab Siamese fighting fish and male antelopes and wildebeests
What do producers provide in a habitat?
The food that supports all consumer species
How are population sizes adjusted in a well-established habitat?
To the amount of food that is available
What can decrease the food supplies of some populations?
Certain environmental factors causing food shortage
What is the main source of food in many habitats?
Plants
What drastically affects plant population size?
Drought
What is the effect of drought on primary consumers?
Food shortage as plants die
What is the effect of prolonged drought?
Primary consumers die or emigrate causing food shortage for secondary consumers and eventually consumers at all trophic levels
What is another factor that can bring about food shortage?
Disease
Give an example of a disease that can cause food shortage
A highly contagious viral disease like rinderpest killing off large numbers of herbivores and causing food shortage for their predators
What are the effects of food shortage?
Decrease in population sizes brought about by competition emigration reduced reproductive rate and increased mortality
What happens during food shortage?
Members of a population compete for the limited food supply with only the most vigorous individuals succeeding
Give an example of competition for food
In a lynx population the fastest runners catch the prey
When does competition between organisms occur?
When other resources in the habitat are limited with food being the most common limited resource
What was shown in the laboratory study of two Paramecium species sharing the same food source?
The more rapidly reproducing P aurelia survived while P caudatum was wiped out
What is the outcome of competition between different species?
The less vigorous species may be eliminated from the habitat
What is emigration?
The movement of members of a population away from its habitat to other areas in response to lack of food or living space
Is emigration a regular or irregular occurrence?
Irregular
Is there a return movement in emigration like in migration?
No
When do individuals emigrate?
Only if their chances of survival are better by doing so than by staying
What do emigrating individuals do?
Join an existing population or establish new populations
Give an example of emigration
Locust swarms
What is the reproductive rate?
The rate at which new individuals are produced
What are examples of reproductive rate?
Birth rate (mammals) rate of egg production (birds) and rate of seed production (higher plants)
What is the effect of food shortage on reproduction?
It lowers the reproductive rate and delays sexual maturity
What happens to clutches and litters during food shortage?
Birds lay smaller clutches and mammals give birth to fewer young
What is retarded during food shortage?
Growth which often delays sexual maturity
What human physiological process is affected by starvation?
Ovulation
What reproductive effects were seen in laboratory rats with inadequate food supplies?
Delayed sexual maturity low sperm production in males and irregular menstrual cycles in females leading to a reduction in births
How do many plants and lower animals reproduce when food is plentiful vs scarce?
Vegetatively when food is plentiful and by seeds and spores when food is scarce
When do seeds and spores germinate?
Only under favorable conditions so the reproduction rate is reduced
What is mortality?
Death rate the number of individuals of a species which die in a given period of time
What is mortality related to?
The average life expectancy of an individual in a species
Describe the three common types of survivorship curves
Type 1 death rate is low until old age Type 2 death rate is constant throughout life and Type 3 death rate is high among the young
What does food shortage increase?
Death rates especially among the young and old
What does Figure 18-9 show?
How a species grows and stabilizes in a new favorable habitat
Describe the stability of an established ecosystem
The various populations or the biotic community are generally stable and in balance
What will be reviewed in this section?
The factors that affect populations and how they contribute to the balance in nature and why human populations seem to defy this balance
What are the abiotic and biotic factors that affect populations?
Abiotic factors include availability of space light heat oxygen water and food Biotic factors include predation competition parasitism diseases natality mortality territorial behavior and dispersal
How are the factors affecting populations categorized?
Some are density-independent and some are density-dependent
How do density-independent factors affect population growth?
They affect it irrespective of population density
Give examples of density-independent factors
Catastrophic events like floods grass fires droughts and storms which often reduce population sizes drastically
How do density-dependent factors affect population growth?
They increase or decrease in intensity as the population density changes
Give examples of density-dependent factors
Availability of food decreasing as population density increases and hormonal changes in locusts causing the development of long-winged offspring that emigrate when population density is high
What do density-dependent factors tend to do to population size?
Keep it fairly stable
Do density-dependent and density-independent factors ever combine to control population size?
Yes
Give an example of combined density-dependent and density-independent factors controlling a population
The number of aphids on a leaf is controlled by competition for food and space (density-dependent) and strong winds dislodging some aphids (density-independent)
Describe seasonal population fluctuations in savanna regions
Plant population increases during the rainy season leading to an increase in herbivore population density due to migration and high birth rates Herbivore population decreases during the dry season due to migration low birth rates and high death rates
What is the primary cause of population fluctuations in savanna regions?
Seasonal variations in rainfall causing cyclic fluctuations
What is the primary cause of population fluctuations in temperate regions?
Variations in temperature causing cyclic fluctuations [cite: 214 215 216 217]
What types of species show population fluctuations that follow flowering and fruiting cycles?
Animal species that feed on the nectar or fruits of plant species [cite: 217 218 219]
Describe population fluctuations in desert annual plants
They survive droughts as seeds and show exponential growth when rains come with the population crashing when the annuals die leaving a new seed crop [cite: 218 219 220 221 222 223 224]
What kind of factor causes the large irregular fluctuations in desert annual plant populations?
A climatic factor [cite: 224 225 226 227 228]
Describe cyclic population fluctuations of brown lemmings in the Arctic tundra
Overgrazing by lemmings as their population increases leads to food shortage causing many to die or emigrate drastically reducing the population and allowing vegetation to recover This cycle repeats [cite: 228 229 230 231 232 233]
Where are seasonal population fluctuations small?
In rain forests tropical lakes and oceans where food supply and most abiotic factors are fairly constant [cite: 233 234 235 236 237 238]
What breeding pattern do species in these stable environments exhibit?
Regular breeding throughout the year [cite: 238 239 240 241]
Where are population fluctuations small due to adaptable diets?
In omnivores [cite: 238 239 240 241]
Why do omnivores have small population fluctuations?
Because food supply does not become limiting even during the unfavorable season [cite: 220 221 222 223 224]
How do predators affect prey populations?
By eating prey they reduce the prey population size [cite: 220 221 222 223 224]
What is the result of predators reducing prey populations?
Increased competition among predators for the remaining prey [cite: 221 222 223 224]
What happens to predator populations as a result of reduced prey?
The less vigorous predators die and the predator population decreases [cite: 222 223 224 225 226]
What happens to prey populations when predator populations decrease?
They increase in size [cite: 223 224 225 226 227 228 229]
What does the increase in prey populations lead to?
An increase in the predator population [cite: 224 225 226 227 228 229]
Describe the relationship between predator and prey population curves
They are similar with the predator curve lagging behind the prey curve and the predator population smaller than the prey population [cite: 227 228 229 230 231 232 233]
What is the biosphere composed of?
many ecosystems [cite: 228 229 230 231 232 233]
What is each ecosystem’s biotic community composed of?
populations of many species [cite: 229 230 231 232 233]
Describe population sizes in an ecosystem with a stable climax community
They are constant but fluctuate around the carrying capacity for each species [cite: 231 232 233 234 235 236]
What does the term dynamic equilibrium mean in this context?
That although the number of individuals in the populations remain constant new individuals are constantly being added and existing ones removed but at equal rates [cite: 233 234 235 236 237]
How is dynamic equilibrium maintained in an ecosystem?
By density-dependent and density-independent factors that increase or decrease the reproductive rate death rate emigration and immigration of each population [cite: 236 237 238]
What happens to equilibrium in a stable community if a new factor is introduced?
It will be upset and the populations will undergo changes in size until a new equilibrium is reached [cite: 237 238 239 240 241]
