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Reproduction Part 2

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The Codfish Strategy

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Up to 9,000,000 eggs/spawn

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**Cod Math The volume of the earth's oceans is 1.35 X 109 cubic Km.**

A typical 50 cm female cod lays 200,000 eggs/yr A typical mature cod might weigh...10 kg Assuming that the fish stack perfectly with no void spaces and that the density of the cod is equal to the density of seawater, then a cubic Km of cod would weigh... (1 cubic km) X (1,000,000,000 cubic m/cubic km) X (1000 kg/cubic m) X to correct for seawater density) = 1.32 X 1012 kg. If a cod weighs 10 kg, then we can calculate the cod fish per cubic km as (1.32 X 1012 kg) X (1 cod/10 kg) = 1.32 X 1011 cod per cubic km of ocean. Then the number of cod that it would take to fill the ocean is equal to (1.32 X 1011 cod/cubic km of ocean) X (1.35 X 109 cubic km of ocean) = 1.78 X 1020 codfish.

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If we assume that the codfish take 5 years to reach their maximum size of 10 kg, that they start spawning at 5 years of age, that each female would lays 200,000 eggs per year once it is 5 years old, and that they live to be at least 25 years old… Year 1: 2 codfish spawn Year 2: ,000 codfish Year 3: (200,000) Year 4: 2 + 3(200,000) Year 5: 2 + 4(200,000) Year 6: 2+ 5 (200,000) + (100,000 X 200,000) Year 7: 2 + 6(200,000) + 2(100,000 X 200,000) Year 8: 2+ 7(200,000) + 3(100,000 X 200,000) Year 9: 2 + 8(200,000) + 4(100,000 X 200,000) Year 10: 2 + 9(200,000) + 5(100,000 X 200,000) +(100,000 X 100,000 X 200,000) 2 + 1,800, ,000,000, ,000,000,000,000,000 = 2,000,100,001,800,000 or 2 X 1015 Year 11: 2(100,000 X 100,000 X 200,000) Year 12: 3(100,000 X 100,000 X 200,000) Year 13: 4(100,000 X 100,000 X 200,000) Year 14: 5(100,000 X 100,000 X 200,000) = 1 X 1016 Year 15: 6(100,000 X X 100,000 X 200,000) + (100,000 X 100,000 X 100,000 X 200,000) = 2 X 1020

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Just 15 Years !

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Mola

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23,000,000 eggs (300,000,000 max!)

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Over the entire lifetime of this mola pair, how many of their babies must survive in order to keep the population stable ? 2

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20 year lifespan 23,000,000 eggs year/mola = 460,000,000 eggs X Need to replace the male and female breeding molas, therefore we need 2 fish out of the 460 million eggs. Mola egg survival to maintain population = 1 per 230,000,000

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Salmon

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10,000 eggs year/salmon 1 year spawning = 10,000 eggs X Need to replace the male and female breeding salmon, therefore we need 2 fish out of the 10,000 eggs. Salmon egg survival to maintain population = 1 per 5,000

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Tiger Shark

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1 baby 2 years/shark 20 year lifespan = 10 baby sharks X Need to replace the male and female breeding sharks, therefore we need 2 fish out of the 10 babies to survive. Shark baby survival to maintain population = 1 per 5

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Two strategies Make bazillions of “low cost” disposable eggs and abandon them. Hardly any survive, but when you start with millions… Make very few eggs with tons of energy and guard them. There aren’t many eggs, but when most are going to survive… R K

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R-selection In unstable or unpredictable environments the ability to reproduce quickly is crucial, and there is little advantage in adaptations that permit successful competition with other organisms, because the environment is likely to change again. R= high fecundity, small body size, short generation time, and the ability to disperse offspring widely. R- Dandelions, mice, grass carp K-selection In stable or predictable environments the ability to compete successfully for limited resources is crucial, and populations of K-selected organisms typically are very constant and close to the maximum that the environment can bear. K= large body size, long life expectancy, and the production of fewer offspring that require extensive parental care until they mature. K-elephants, whales, Arctic Terns, tiger sharks

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**R (many eggs): Unstable environments**

R (many eggs): Unstable environments. Many years things go wrong and the population drops, but in good years fry survival is high and the fish population can explode. K (few eggs): Stable environments. Many animals competing with each other for resources. Difficult to find an opportunity for a big population increase, and they would probably starve anyway.

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**R or K ? River Unpredictable flow Unpredictable plankton blooms**

Unpredictable water temps Unpredictable oxygen levels! R or K ?

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**Coral Reef Stable temperatures Stable water quality Consistent plankton populations**

R or K ?

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**R or K ? Shallow temperate seas Unpredictable plankton blooms**

Unpredictable water temps

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**R or K ? Deep Sea Constant water temp Constant water quality**

Stable food supply

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**? Intermediate Strategies K R Stable tropical seas**

Large well-developed young Live bearers ? R Unpredictable conditions for fry Egg broadcasters- huge numbers

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**Other strategies for the Kish crowd**

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**Kurtus gulliveri the Nursery Fish**

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**Kurtus gulliveri the Nursery Fish**

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**Males carry eggs in clusters or balls attached to a hook on the head**

Males carry eggs in clusters or balls attached to a hook on the head. This may be an adaptation to environments with low oxygen and high turbidity

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Snailfish

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Snail Fish Eggs

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Bitterling

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Bitterlings At Work

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Seahorses

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**Sharks, Rays, and Ratfish**

Truly Special K

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Internal Fertilization

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Egg Layers are "oviparous"

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Ratfish

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Cownose Ray

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Eagle Ray

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Manta

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Stingray

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Torpedo

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Chevy Stingray

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Oviporous Mating Strategies

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Oviporous Eggs

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Skate Egg Shark Egg

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Mermaid’s Purse

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Port Jackson Shark

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Oviviparous: eggs hatch in females and embryos hang out and grow

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Smooth Dogfish

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Porbeagle Shark

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**Another Oviviparous Strategy**

Baby sharks swim in the mother and get nutrients by drinking the uterine fluids

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Viviparous: Like mammals. Placenta-like structure

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Uterus Like Sac Shark Embryos Placenta like structures carrying blood

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Special (and nasty) Tiger Shark Reproduction (oviparous)

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Shark embryos in eggs

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The mother shark feeds unfertilized eggs to the babies.

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The mother shark feeds unfertilized eggs to the babies.

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Tiger Shark 1 of 5 must survive

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**Two basic strategies R K**

Make bazillions of “low cost” disposable eggs and abandon them. Hardly any survive, but when you start with millions… Make very few eggs/babies with tons of energy and guard them. There aren’t many eggs, but when most are going to survive… There are plenty of intermediate strategies R K

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**Many Approaches Oviparous: Egg layers**

Broadcasters Parental care Oviviparous: Eggs hatch inside female Viviparous: Placenta-like arrangements

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Reproductive strategies for Survival

Reproductive strategies for Survival

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