Evolution is a long and intricate process that involves adaptation and species interaction as well as environmental variables. As an example lets just say spider web is red, the spiders traditional prey cannot see red so he eats well. The prey species has a few members who mutate and see red so these few do not get eaten. They have little red seeing babies that also grow up and have lots of babies until eventually all surviving members see red. Many spiders starve but a few have babies that spin pink webs....the prey cannot see the pink so well so these spiders eat pretty well and have lots of babies, a few of which make faded pink webs. Rinse and repeat until pink fades completely and webs become clear. Now we have well fed spiders and insects that cannot see their webs but in a thousand generation they will see the webs and spiders will evolve something new.
You are correct that if a predator species kills off all of the prey that it depends upon to survive then it too will go extinct. If you look at predators like lions and their prey species like zebras there is a fixed ratio between them that applies across all types of wildlife including fish where this ratio probably originated. http://www.iflscience.com/plants-and-animals/universal-pattern-governs-ratio-predators-prey/ First thing to consider is that for the prey to survive they need a food source. When their food is abundant their numbers increase and when it is scarce their numbers decrease. Predators follow the same pattern but in a different proportion. If the number of zebras doubled the number of lions would only increase by a ratio of 1.7. There are multiple factors involved but to keep it simple the cost of raising predators is higher than the cost of raising prey. Walking around and eating vegetation that can't run away does not expend the same degree of energy as having to find, stalk, chase and kill your food. With the above explanation in mind let's get back to those spiders. Making a web is an expensive and time consuming process as is keeping it in working order given damage from various sources such as the weather. Putting up a web where there are no prey insects means that choosing the right location is important and that exposes the web to damage too. How many insects are not caught in a web because a passing animal, like a zebra, damaged the web before the flies on it's back could be caught in the web? Compare all that work the spider has to do to get a meal to the work their prey insects like flies have to go through. The flies catch a ride on the zebras and wait for them to take a crap. Bingo, a hot meal, sex, and a safe place for the larvae to spawn. Did I mention the issues that spiders have to deal with in order to find a mate? Males have to go searching for females which means that they are no longer catching any prey for themselves. In some species they have to fight other males in order to procreate. Being a spider is harder than Spiderman makes it look. So the answer is in the ratios of predators to prey and how much work is involved in order to survive and procreate.
The horses (with riders) almost always win the man vs. horse marathon in Wales. Humans have only won twice in 38 races, both times on hot days. https://en.wikipedia.org/wiki/Man_versus_Horse_Marathon Running down a large animal until it drops from heatstroke really only works in hot climates. Wounding it first isn't really running it down. In cooler climates, the preferred strategy was to run the prey into other hunters, or into a trap or over a cliff.
I am guessing that the next web is not recycled since the material we call silk comes from inside the spider body. Fascinating also is what do spiders eat that can turn into silk?
I would love to see humans race horses at the Kentucky Derby. Since horses run at over 40 miles per hour, a human has to be much faster over distance than Usain Bolt is.
Reminds me of back when I was a mere lad, and I came home with a hunting pouch full of rabbits. I saw lots of them that day and harvests several. I was telling my dad about the number I had seen, and he told me that meant the fox population that year was lower than other years. If you see lots of rabbit, there are fewer foxes, if you see fewer rabbits, there are more foxes. So during trapping season you could expect to trap more fox when the rabbit numbers are lower. That it always worked out in this manner told me he might be onto something.
move that into a mall/grocery store and you'll see hunter gatherer behaviour...women wandering around examining, touching everything even things they didn't intend to buy, the men will trail behind checking out other people(danger) ready to give a hand if required...when men shop they tend to be direct, they have their intended prey and are focused on only that until they make their purchase/kill and then head back home...
Uhh, yeah....... Fat unfit men and women waddling around smoking and shopping, nothing like traditional hunters of old.
