Ecosystems, Year 9: People and the environment

Bioaccumulation

提示The first part of the word means life; the rest means piling up.

为什么Some poisons cannot be broken down or excreted, so they stay in an animal's tissues and the store grows throughout its life. Each animal also eats many of the organisms below it, so the amount stored is larger at every step of a food chain, and the animals at the top carry the most.

They are not broken down or excreted, so they stay in the body

提示Ask where a substance ends up if an animal can neither digest it away nor get rid of it.

为什么A toxin that is broken down, or passed out in urine, never has the chance to collect. The dangerous ones last: DDT, for example, dissolves in body fat and stays there for years, so every contaminated meal adds to the store.

200

提示None of it leaves after each meal, so every fish adds to the running total.

为什么Each fish hands over its whole store and the heron keeps all of it. That is why a top predator can carry hundreds of times more toxin than the animals it eats, even when the water holds only a trace.

Through their food — the birds they hunted carried it

提示Peregrines catch pigeons, and pigeons feed on farmland grain.

为什么Seed-eating birds picked up small doses from treated grain, and each peregrine ate many of those birds. The pesticide built up in the falcons until their eggshells grew thin and broke. Numbers recovered after these pesticides were banned.

Greys outcompete them for food and carry a virus that kills reds

提示The newcomers are bigger, eat the same nuts and seeds, and arrived with something invisible.

为什么An introduced species can upset a food web that took thousands of years to settle. Grey squirrels take the food red squirrels need and carry squirrelpox, which does them no harm but is deadly to reds. Red squirrels now survive mainly where greys are rare or absent.

It falls, because the parents cannot find enough food

提示Follow the link in the web: take away what the chicks are given to eat.

为什么Removing one species from a food web affects everything that feeds on it. Seabirds such as puffins and kittiwakes depend on sandeels, which is why large-scale sandeel fishing was closed in the English North Sea and in Scottish waters in 2024.

They lost their nesting sites, shelter and food

提示Think about everything a dense, berry-covered hedge offers a small bird.

为什么A hedgerow is a habitat: it supplies berries, seeds and insects to eat, cover from predators and safe places to nest. Changing how land is used removes habitats, and the species that depended on them decline even though nobody harmed them directly.

Few ladybirds are left to eat the aphids

提示Think about which of the two insects was keeping the other in check.

为什么Aphids reproduce extremely quickly, so the few that survive the spray can rebuild their numbers within weeks. Their predators recover far more slowly. With little left to hunt them, the pests return in greater numbers, which is one reason farmers are encouraged to protect natural predators.

Young fish escape and survive to breed

提示Ask what size of animal slips through a bigger hole, and what it can go on to do.

为什么If fish are caught before they are old enough to reproduce, the population cannot replace itself and it collapses. Letting the small ones through leaves enough breeding adults for the future, so fishing can continue without wiping the stock out.

Nature conservation

提示The second word is also used for looking after old paintings and historic buildings.

为什么Conservation covers anything done to stop species and habitats being lost: protecting land as nature reserves, controlling hunting and fishing, breeding rare animals and storing seeds. The aim is to keep populations large enough to survive on their own.

Protecting a habitat protects every species living in it

提示Count how many kinds of plant, insect, bird and fungus share a single wood.

为什么A zoo can hold a few hundred kinds of animal; a woodland holds thousands of species, most of them small and unnoticed, along with all the feeding links between them. Species cannot survive in the wild without somewhere suitable to live, so saving habitats comes first.

Reintroduction

提示It means bringing a species back to a place where it used to live.

为什么Red kites were wiped out across most of Britain by persecution. Releasing birds into suitable habitat, and protecting them by law, let breeding populations build up again. The method only works once the original cause of the decline has been removed.

To keep each species' genetic material safe in case it dies out in the wild

提示Think of it as a backup copy, stored somewhere the original cannot be damaged.

为什么A gene bank stores seeds, eggs, sperm or tissue so that the hereditary material of a species is not lost. If a plant becomes extinct in the wild, stored seeds can be grown to bring it back, and breeders can use them to add useful features to crops.

endangered

提示It is the stage a species reaches before the word used for the dodo.

为什么Scientists assess how many individuals are left and how fast numbers are falling. Species judged to be at high risk are listed as endangered, which helps governments and charities decide where conservation effort and money are most urgently needed.