Unit 2.6 Changes in Populations DP Biology 12 Unit 2.6 Changes in Populations

2.6.1 Explain the concepts of limiting factors and carrying capacity in the context of population growth.

Populations Factors affecting population size Natality Mortality Birth rate Mortality Death rate Immigration Rate at which individuals join the population Emigration Rate at which individuals leave the population

Populations Factors affecting population size

Populations Carrying capacity In nature population sizes can not grow infinitely due to limiting factors Disease Parasites Accidents Disasters Hunting and predation Competition for resources Limit to available resources

Populations Carrying capacity The maximum number of organisms of a given species that a habitat can support without environmental degradation Represented as “K”

2.6.2 Describe and explain S and J population curves.

Populations J-curves Many populations are capable of exponential growth Doubling at a predictable rate Graphed on a J-curve

Populations Sigmoid growth curve

Populations Sigmoid growth curve When populations move into a new environment, they follow a very predictable pattern of development: Exponential phase Transitional phase Plateau phase

Populations Sigmoid growth curve 3 2 Population Size 1 Time

Sigmoid growth curve Population is expanding into a habitat offering initial low limiting factors Exponential Phase of rapid population growth rate Slowing yet still high growth rate against time or generations Plateau stage when the population remains stable with time There maybe slight oscillations

Populations Sigmoid growth curve Exponential phase Population doubles per unit time producing exponential/geometric growth No limiting factors Nutrients, oxygen, space in ample supply Does NOT mean no death or emigration! Examples: Germinating annual plants in a new season Bacteria during the initial phases of an infection

Populations Sigmoid growth curve Transitional phase Population growth continues, but at an ever-decreasing rate Limiting factors slow growth rate Nutrients, oxygen, space in ever-shorter supply More selection (survival and reproduction) of those individuals within the population best suited to accessing the resources

Populations Sigmoid growth curve Plateau phase Population growth slows to zero (stable) Limiting factors inhibit growth Nutrients, oxygen, space in short supply Natality + Immigration = Mortality + Emigration Population size is determined by the carrying capacity of the habitat How large a population it can support

Populations Comparison

Populations Comparison In nature, J-curves often become S- curves over time Environmental resistance = the effect of factors that limit population growth Some species experience exponential growth when conditions are good, then die-back below the K

Populations

2.6.3 Describe the role of density‑dependent and density‑independent factors, and internal and external factors, in the regulation of populations.

Populations Factors limiting population growth With unlimited resources, populations would increase exponentially In reality, environmental resistance limits the population growth Determines the carrying capacity of habitat

Populations Factors limiting population growth Density-dependent factors: Depend on the size of the population Become greater as population grows Act as negative feedback

Populations Factors limiting population growth Density-dependent factors: INTERNAL – within a single species Competition Reduced fertility Shortage of food or prey Accumulation of waste Shortage of space or territory Mortality due to disease Predation or parasitism

Populations Factors limiting population growth Density-dependent factors: EXTERNAL – between species Mortality due to disease Predation or parasitism

Populations Factors limiting population growth Density-independent factors: Do not depend on population size Tend to be abiotic

Populations Factors limiting population growth Density-independent factors: Mortality due to weather Mortality due to natural disasters

2.6.4 Describe the principles associated with survivorship curves including, K‑ and r‑strategists.

Population ecology Reproduction strategies Natality has a strong affect on population size Different animals have different reproductive patterns to be fit Two main reproductive strategies: r-strategies K-strategies

Population ecology Reproduction strategies r-Strategies Reproduce very rapidly Produce a large number of offspring Low parental care Short generation time Short lifespan

Population ecology Reproduction strategies r-Strategies Pioneer organisms Move into new habitats Migration and dispersal are important Achieve rapid colonization Often small organisms Breed quickly

Population ecology Reproduction strategies r-Strategies Unstable habitats Environment changes quickly Larger population may have more variation Easier to adapt More likely that some survive Easier to restore large population If many die during a disturbance J-curves!

Population ecology Reproduction strategies r-Strategies Examples: Many insects Many rodents Weeds Some fish

Population ecology Reproduction strategies K-Strategies Reproduce slowly Produce few offspring High parental care Have a long life span Constant population size Near carrying capacity Compete successfully for resources Often near carrying capacity (K)

Population ecology Reproduction strategies K-Strategies Stable habitats Adapted to competition for resources Specific adaptations and behaviors Invest into young to help them be fit Smaller population Near carrying capacity – S-curves! Often larger organisms

Population ecology Reproduction strategies K-Strategies Examples: Large mammals Some birds

Population ecology

Population ecology Reproduction strategies r/K-Strategies Most animals somewhere in-between Some organisms are at extremes Display some r-traits and some K-traits

Do humans follow r- or K- strategies? TOK QUESTION: Do humans follow r- or K- strategies? There are many stereotypes and ideas about how socioeconomic class and international cultures affect how people raise their children. How can this be explained using the concept of reproductive strategies in population ecology?

2.6.5 Describe the concept and processes of succession in a named habitat.

Ecosystems and biomes Succession Ecological succession Process of colonization when new land is made available A sequence of different communities (sere) Transition from first colonizers to most “fit” Goes through several stages (seres) until reaching a climax community

Ecosystems and biomes Succession Ecological succession Xerosere Succession on land Hydrosere Succesion in water

Ecosystems and biomes Succession Two types: Primary succession Succession beginning on completely new land without established soil (prisere) Secondary succession Succession beginning on existing soil Site has sustained life before

Ecosystems and biomes Succession Primary succession New land is formed: Dried river deltas Overturned sand dunes Cooled lava New exposed rock (erosion) New water is collected: New pond formed (flooding or rain)

Ecosystems and biomes Succession Primary succession Site has never sustained life before First step is always to create soil

Ecosystems and biomes Succession Primary succession Example: In 1980, Mount St. Helens in America erupted 57 people and thousands of animals were killed Hundreds of square kilometers were destroyed

Ecosystems and biomes Succession Primary succession Example: In 1980, Mount St. Helens in the USA erupted 25 years later, plants and animals are coming back

Ecosystems and biomes Succession Primary succession Example:

Ecosystems and biomes Succession Primary succession Mosses and lichens break down rocks Using acid Creates small amounts of soil First colonizers die Detrivores break them down Adding nutrients and minerals to the soil Can take many years

Ecosystems and biomes Succession Primary succession More plants will be able to grow Hold the soil with their roots Can not blow away Minimizing erosion and water-loss Breaking wind and creating shadow Attracts consumers Come to eat the plants

Ecosystems and biomes Succession Primary succession

Ecosystems and biomes Succession Primary succession Over time: Diversity increases Productivity increases

Ecosystems and biomes Succession Primary succession Bare, inorganic habitat Colonization Establishment Competition Stabilization Seral climax

Ecosystems and biomes Succession Secondary succession Site has sustained life before Soil is present Usually happens very quickly Land is destroyed: Forest fires Hurricanes/typhoons/cyclones Deforestation

Ecosystems and biomes Succession Secondary succession Example Fires burn down forests ie. Near Athens, Greece in 2007 Burned vegetation adds nutrients to the soil

Ecosystems and biomes Succession Secondary succession Example Once fire goes out, seeds are blown back in Many resources and little competition

Ecosystems and biomes Succession Secondary succession Example

Ecosystems and biomes Succession

2.6.6 Explain the changes in energy flow, gross and net productivity, diversity and mineral cycling in different stages of succession.

Ecosystems and biomes Succession Gross productivity The rate of production of new biomass Increases through succession

Ecosystems and biomes Succession Gross productivity Low during early stages Few produces No soil for new growth High in later stages More producers

Ecosystems and biomes Succession Net productivity GP – R (respiration = energy used)

Ecosystems and biomes Succession Net productivity High during early stages System is adding biomass Little energy lost as numbers are low and little competition Falls in later stages More respiration as more energy needed to compete without adding new biomass Ratio of GP:R approaches 1:1

Ecosystems and biomes Succession Biodiversity Species richness!

Ecosystems and biomes Succession Biodiversity Low during early stages Few pioneer species can live on bare rock Few producers = little food for consumers High in later stages Food webs become more complex Pioneers still survive, but new species immigrate Falls slightly at climax Specialized niches with high competition Pioneers are out-competed (competitive exclusion)

Ecosystems and biomes Succession Mineral cycling Low during early stages Few producers to break down rock Limited time for erosion Limited soil for decomposers Increases throughout succession Remains high Especially in hot tropical zones

2.6.7 Describe factors affecting the nature of climax communities.

Ecosystems and biomes Subclimax community Often a factor prevents succession from reaching climax Climate or lack of nutrients Later species can not survive as niches lacking or too few nutrients or soil Succession is “stuck” until limiting factor is removed

Ecosystems and biomes Zonation Set of habitats in different seral zones due to gradient of some limiting factor Pioneer species in a forest when an old tree falls Distance from the beach as sand dunes are blown by wind Distance from ocean as salinity decreases Altitude as temperature drops

Ecosystems and biomes Plagioclimax Humans can maintain highest productivity of early stages Maximize NP by limiting R

Ecosystems and biomes Plagioclimax Preventing waste of energy Cut crops as soon as they mature to limit time of competition Prevent other species from competing Prevent natural predators, diseases and parasites Maintain optimal conditions for growth

Ecosystems and biomes Plagioclimax Much of Europe is kept in a permanent “plagiosere”