Ch 6 – Population Ecology Special Topics These lectures contain copyrighted images that are provided in the teacher materials for Friedland/Relyea Environmental Science for AP Textbook. By using these lectures, you guarantee that you have legal access to these images or that you have replaced the copyrighted images with images that you have the rights to use.

Population Characteristics Why it matters Example Size Helps us understand how healthy the population is CA condor population reached a critical low of 22 triggering the captive breeding program Density Helps us understand how the population works together, how to protect them and how to manage resources and protections Population densities can help us manage fish populations by setting limits in certain areas or designated MPAs Distribution Clumped is the most common because resources are often clumped. Sex ratio Varies by specie, but large imbalances can be concerning China male : female ratio. Male preference has led to a sex imbalance in China which is resulting is social consequences Age Structure Helps us understand how fast a population will grow. Lots of young usually indicates growth and lots of old indicates shrinking The Amur leopard population currently has less than 20 adults and only 5-6 cubs indicating a serious decline

Biotic Potential Factors that encourage a population to increase under ideal conditions, potentially leading to exponential growth Abiotic Contributing Factors: Favorable light Favorable Temperatures Favorable chemical environment - nutrients Biotic Contributing Factors: High reproductive rate Generalized niche Ability to migrate or disperse Adequate defense mechanisms Ability to cope with adverse conditions Results in a J curve Cannot be sustained over a long period of time because resources are limited

Environmental Resistance All the factors that act to limit the growth of a population Abiotic Contributing Factors: Unfavorable light Unfavorable Temperatures Unfavorable chemical environment - nutrients Biotic Contributing Factors: Low reproductive rate Specialized niche Inability to migrate or disperse Inadequate defense mechanisms Inability to cope with adverse conditions Results in an S curve once carrying capacity is reached Populations that grow too fast may experience an overshoot and die-off

Metapopulations When isolated populations have some level of interaction Occasional immigrants from larger nearby populations can add to the size of a small population and introduce new genetic diversity The number of species that exist as metapopulations is growing because human activities have fragmented habitats, dividing single large populations into several smaller populations. Identifying and managing metapopulations is thus an increasingly important part of protecting biodiversity.

Isle Royale Case Study http://www.wbir.com/video/2751732909001/1/The-plight-of-the-wolves-of-Isle-Royale Top down population control – when predators keep a population from growing as large as it could Bottom-up population control – when food availability keeps a population from growing as large as it could http://www.isleroyalewolf.org/

Occupying the same niche Partial niche overlap both compete in the overlapping parts of the niche. If the overlap is minimal, both species can coexist by specializing. Called resource partitioning. Full niche overlap both compete directly for the same resources One specie will be more suited and out-compete the other specie Called the Competitive Exclusion Principle http://zoology.muohio.edu/oris/cunn06/cs6_04.htm, http://www.biologycorner.com/APbiology/ecology/ch47_communities.doc

Resource Partitioning Examples

Mutualism Species Interactions The tickbird is eating the ticks off the zebra.  This partnership feeds the bird and keeps the zebra from having ticks sucking on it. What type of relationship is this? Mutualism

Species Interactions Predation The seal has hunted and captured the penguin for dinner What type of relationship is this? Predation

Species Interactions Mutualism The anemone fish lives among the forest of tentacles of an anemone and is protected from potential predators not immune to the sting of the anemone. The fish increases the water flow and provides more food for the anemome. What type of relationship is this? Mutualism

Species Interactions Barnacles live on Grey Whales without harming the whale. Barnacles benefit because they feed on the water as the whale swims. Commensalism http://www.learner.org/jnorth/tm/gwhale/Hitchhikers.html

Species Interactions Parasitism The deer tick feeds off of the blood of mammals and often transmits diseases such as lyme disease. What type of relationship is this? Parasitism

Keystone Species Sea Otters Elephants http://www.youtube.com/watch?v=0UryWICizN4 Predator-mediated competition Elephants http://ca.pbslearningmedia.org/resource/5071aea2-7262-4af2-894e-9d3af57d34f5/5071aea2-7262-4af2-894e-9d3af57d34f5/ Ecosystem engineers

Succession Succession is a series of changes that occur as an ecosystem develops Initial species are called pioneer species – they set the stage for the appearance of other species eventually resulting in a climax community. Primary succession that occurs on newly formed soil ex.: volcanic flows, glacier movement, etc Secondary Succession that occurs post an ecological disruption Ex: post mining, post fire, post flood

Ecological Succession http://bcs.whfreeman.com/thelifewire/content/chp55/55020.html

Human Impacts on populations Fragmentation and degrading habitat Simplifying natural ecosystems (monocultures) Interfering with primary productivity, thus altering food webs Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides Elimination of some predators Introduction of non-native species Over-harvesting of renewable resources Interfering with nutrient cycles Over dependency on non-renewable resources

Population Equations Pop Change = (births + immigration) - (deaths + emigration) The growth rate is the rate at which a population is growing. Growth Rate (%) = Birth Rate - Death Rate 10 Birth rate = # of live births per 1000 Ex: if 50 babies are born per 1000 people, then the birth rate is 50. Death rate = # of deaths per 1000 Ex: if 25 people die per 1000, so the death rate is 25. Current Population size = Pop0 + (b + i) - (d + e) Zero Population Growth : (b + i) = (d + e) Nt = Noert (requires calculator so won’t be on AP EXAM!) Doubling Time = 70/Growth Rate (%) (no calculator needed)

Exponential growth is not realistic due to limited resources - Carrying capacity – the maximum number of individuals an ecosystem can support over a given period of time due to environmental resistance - Overshoots - usually occur due to a time lag – it takes time for the birth rate to fall and the death rate to increase http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/environment/populationsandpyramidsrev6.shtml

Reproductive Strategies Goal of every species is to produce as many offspring as possible Each individual has a limited amount of energy to put towards life and reproduction This leads to a trade-off of long life or high reproductive rate Natural Selection has lead to two strategies for species: r - strategists and K - strategists r-strategists K-strategists Focus on reproduction Insects, bacteria, mice, rabbits Have lots of offspring, but most will not survive to adulthood Short period of time between birth and reproduction Focus on a long life Elephants, humans, redwoods Have few offspring and take care of them for a long time Long period of time between birth and reproduction

R strategists Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate Population size fluctuates wildly above and below carrying capacity (boom and bust) Generalist niche Low ability to compete Early successional species

K-strategist Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate Population size fairly stable and usually close to carrying capacity Specialized niche High ability to compete Late successional species

Survivorship Curves Late Loss: K-strategists - few young - care for young until reproductive age - lowjuvenile mortality Constant Loss: intermediate reproductive strategies with constant mortality (birds) Early Loss: r-strategists - many offspring - high infant mortality - high survivorship once a certain size/age