G.5 Population Ecology Van Roekel IB BIO II 4/29/15

Assessment Statements G.5.1 Distinguish between r-strategies and k-strategies G.5.2 Discuss the environmental strategies that favor either r-strategies or k- strategies G.5.3 Describe 1 technique used to estimate population size of an animal species based on mark-release-recapture method G.5.4 Describe the methods used to estimate the size of commercial fish stocks G.5.5 Outline the concept of maximum sustainable yield in the conservation of fish stock G.5.6 Discuss international measures that would promote conservation of fish

R-Strategies vs. K-strategies Continuum of strategies for caring for species R-Strategy – strategy of disposable offspring Produce multiple (up to thousands) of eggs/offspring that need little care from parents Insects, Zebra Muscles, etc… K-Strategy – strategy of nurturing offspring Organisms have fewer offspring and spend considerable time and energy caring for them Elephants, Zebras, Humans Some organisms fall in between the two extremes Ducks – lay multiple eggs because some may be eaten by predators, but ducklings need parental care.

R-Strategies vs. K-strategies Characteristic R-strategy K-Strategy Life Span Short Long Number of Offspring Many Few Growth Quickly Slowly Onset of Maturity Early Late – after a long period of parental care Body Size Typically Small Typically Larger Reproduction Once during lifetime More than once during lifetime Parental Care None Very likely and in depth Environment Unstable Stable

Environmental Conditions that favor R-strategy Unstable environments favor organisms that produce many offspring as quickly as possible. Many offspring can be lost to unpredictable forces Few that remain can reproduce and carry on genes or species Ecological disruptions favor r-strategists Able to grow quickly and take advantage of disruption before other organisms Plants on foredune, where shifting sand and salt spray cause unstable conditions use this strategy. Weeds produce thousands of seeds and grow quickly to take advantage of unstable environments

Environmental Conditions that favor K-strategy Stable environments favor organisms that care and nurture their offspring Area is more predictable and less susceptible to unknown forces More effective to invest resources in becoming more competitive Mature dune is not susceptible to wind or salt spray and the soil has been built up over hundreds of years. Organisms invest more in being competitive in a stable environment to make the most of the available resources.

Capture-Mark-Recapture Sampling technique that enables one to estimate the number of animals in an ecosystem Catch some organisms within a population and mark them (tags, chips, etc.) Release marked animals back into environment and allow them to interact w/ population Recapture a second group of individuals from the same population, some will be marked, others will be unmarked Use the proportion of marked to unmarked individuals to estimate size of population The proportion of marked to unmarked individuals in second capture is equal to the proportion of originally marked individuals to whole population

Capture-Mark-Recapture formula (Lincoln Index) Population Size (N) = (n1 x n2) / n3 Population Size = total population n1= number marked in first sample n2= total caught in second sample n3= number marked in second sample

Example Suppose you capture and mark 100 grasshoppers and release them back into the wild. Then you capture another 100 grasshoppers and 10 of them are marked. What is the estimated population size of grasshoppers? N = (100 x 10) / 100 N = 1000 grasshoppers

Use of Lincoln Index Two Primary uses Can be used to compare populations of different species at one time Chart the change in a species of population over time

Limitations to Capture-Mark-Recapture Take caution to avoid the following: Marks may injure animals Marks may make them more visible to predators Marks may make them unattractive to opposite sex Method assumes population is closed (meaning no immigration/emigration. This rarely happens)

Estimating Size of commercial fish stocks For the North Atlantic Ocean, Scientists from ICES (International Council for Exploration of the Sea) are sampling fish, measuring: Type of fish, Age, Length, Breeding Conditions Use information to predict size of commercial fishing stock

Estimating Size of commercial fish stocks – Gathering Information From Fishers (collect info onboard fishing vessels) Number and kinds of fish thrown back Tagging and releasing fish Questioning fishers about perception of catch Reviewing logbook data, which gives catch-per-unit-effort (increased effort for same catch indicates a decrease in population numbers)

Estimating Size of commercial fish stocks – Gathering Information From Research Vessels Cast nets in hundreds of selected location (trawling) for samples Echo sounders to locate schools of fish in order to determine biomass and numbers of fish populations Calculating age by counting number of otoliths (ear bones), or measuring the rings of fish scales Too few young fish indicates lack of spawning Too few old fish indicates over-fishing Using coded wire tags (capture-mark-recapture method) to estimate total population

Estimating Size of commercial fish stocks – Analyzing Date Mathematical models are used to turn all this data into usable data that can be used by the fishing industry and governments to regulate and plan for the future of fish in the oceans and lakes.

Maximum Sustainable Yield Maximum Sustainable Yield (MSY) is the highest proportion of fish that can be removed from the total population without jeopardizing the maximum yield in the future If fish stock is too small, there are not enough adult fish to produce sufficient young fish. Fishing from a stock that is too small leads to over-fishing If fish stock is too large, the annual reproductive rates may be low because of increased competition for food.

International measures to promote conservation of fish In 2006, it was found that all seafood species had declined by 29% in the last three years If the trend continues, by 2048 there would be no more commercial fishing The following would promote the conservation of fish and reverse the current decline

International measures to promote conservation of fish Regulate bottom trawling of the ocean (strip mining of ocean floor) Rebuild depleted fish populations as quickly as possible and pay attention to MSY Eliminate wasteful and damaging fishing practices (trapping unwanted animals in fishing nets reduces biodiversity) Enact strong national fishing quota programs according to MSY Establish programs to develop less damaging fishing gear (shrimp nets that have trap doors to release unwanted animals) Provide funds to improve scientific research which counts fish populations and monitors catch Encourage relationships between fishers and scientists Establish marine reserves and no-catch zones to improve biodiversity and increase fish stock in protected areas

International measures to promote conservation of fish-difficulties Enforcement and monitoring such regulations is difficult International trust does not exist to keep these practices functioning Prices for fish around the world has risen Encourages fishing for scarcer fish Catching the big fish eliminates the specimens which lay the most eggs Difficult to tell fishers to limit their catch when many are going out of business.