It’s in your nature: Overreproduction?
The American toad is a coldblooded animal that returns to a water source in spring, lays its eggs and then retreats to it terrestrial home, offering no care for eggs or offspring. BARRY REED/SPECIAL TO THE TIMES NEWS
A few weeks after the toad eggs are fertilized, small black tadpoles hatch. They face a gantlet of predators, and hopefully a few will survive the weeks until they leave the water.
“Nature” appears to provide enough tadpoles to survive to become an adult, yet still provide vital food for birds such as this migrating solitary sandpiper, which feasted on a few of the tadpoles.
Turtles, such as this 15-inch snapping turtle, “only” lay 30 or more leathery eggs, hoping that a few go undiscovered by hungry raccoons or opossums in hopes that a few hatch and make it safely back to water.
Hundreds of toad tadpoles swarm a spring puddle a week after hatching. They face many predators, and hopefully a few will survive the weeks until they leave the water.
Birds and mammals are homeothermic (warm-blooded), and both utilize their innate trait of parental care. Parental care is responsible for smaller offspring numbers in these two classes. Mammals, at least many of them, have one or two offspring. Mammals have perfected parental care by nursing, warming, nurturing and protecting their young; ensuring a much higher survival rate.
Altricial birds (such as robins) lay four or five eggs, incubate them, protect and feed young, and once fledged, care for them for another 10 days. Precocial birds (turkeys, geese) may have clutches of 12 to 15 eggs, they incubate them, but soon after hatching, the fully feathered miniatures of the parents move about on their own. However, these poults/goslings are exposed to much more danger and the elements than a “robin” and probably only four or five of that clutch grow to adults. Even with parental care, about 2/3 of the offspring don’t “make it.”
That is why their clutches are rather large.
But the Poikilothermic (coldblooded animals) and most insects don’t innately have the parental care trait. They generally have no role in their offspring’s success after laying the eggs. The result is fish, amphibians, reptiles and most insects need to lay immense numbers of eggs.
A trout or salmon may lay 3,000 to 6,000 eggs on a stream bottom where they can be eaten, damaged or washed from the gravel to be smothered in silt. Some eggs aren’t fertilized or the fry get diseases, are eaten or starve. Only three or four may survive to reach reproductive age.
Toads or frogs employ much the same technique. They may lay 5,000 to 6,000 eggs in a puddle, stream or vernal pool and then essentially desert them. There is no parental care.
These amphibians species rely on the fact that statistically, a few of all of those eggs will be “lucky” enough to survive. First the eggs need to hatch and not be exposed to drought conditions or predators. Once hatching, they need to avoid a gantlet of predators from underwater insects, crayfish, herons, raccoons, grackles and other amphibians. (You get the picture.)
Most reptiles, turtles for example, have improved the egg survival chances, by having a leathery covering on their eggs. This at least protects the eggs from drying. Because of this, a snapping turtle may lay “only” 30 or more eggs in a shallow pit dug into a bank. Unfortunately, prowling raccoons probably discover 75 percent of these nests, and the eggs get eaten. Somehow, a nest or two is not discovered and a few 2-inch hatchling turtles must avoid predators and find a pond. Some will survive.
Mayfly adults may only live an hour. They are the survivors of thousands of eggs that were deposited on a stream a year earlier. Again, statistically a few always “make it.”
To conclude, the lesser-developed species, in order to survive, need to produce many eggs, hoping that a few will indeed survive to perpetuate the species.
Test your outdoor knowledge: Ferns will soon be sprouting all over our forests. Which fern species is the most likely to survive in rather dry conditions? A. wood fern, B. sensitive fern, C. Christmas fern.
Last week’s trivia: Red, black, and scarlet oaks all have pointed lobes; chestnut oak leaf lobes are not.
Contact Barry Reed at firstname.lastname@example.org.