Every species has its place in nature, but cer­tain crit­ters have out­sized impacts on the ecosys­tems around them. Here are some that may be liv­ing near you. Ecol­o­gists call them key­stone species; through some fair­ly sub­tle actions, they have a pro­found effect on every­thing around them.

The Beaver
Unas­sum­ing, over­sized rodents with slap-hap­py tails, beavers make up in engi­neer­ing skills what they lack in claws, speed, or climb­ing abil­i­ty. Their dam-build­ing skills are designed to cre­ate a pond where they can dive away from preda­tors and access their lodge from under­wa­ter. In the process, they fun­da­men­tal­ly alter the world around them. They turn swift flow­ing streams into still ponds with deep water. River­side forests become man­grove-like swamps, which changes the com­po­si­tion of the for­est edges. Even­tu­al­ly, beaver ponds become wet mead­ows. Beavers are also vora­cious enough eaters to fun­da­men­tal­ly change the species that grow to fill the mead­ows they create.

Sea Otters
Cute and fuzzy, the pho­to­genic sea otter is one of the biggest eco­log­i­cal cat­a­lysts on the plan­et. Lack­ing blub­ber, they eat con­stant­ly to keep warm in the cold oceans of Cal­i­for­nia, Wash­ing­ton, British Colum­bia and Alas­ka. They eat sea urchins, and a lot of them. Where they’re absent, hav­ing been hunt­ed for fur in the 1800s, the urchins have run rampant—eating vital kelp forests down to noth­ing. The kelp forests serve as nurs­eries for many species of fish, and also grow thick enough to block waves from hit­ting the coast. Rein­tro­duc­tion of sea otters has sparked the regrowth of kelp forests—which is now chang­ing the way waves hit exposed shore­lines, chang­ing pat­terns of inter­tidal life.

The Gray Wolf
An apex preda­tor, the Gray Wolf’s rein­tro­duc­tion sent a wave of effects through Yel­low­stone Nation­al Park in the 1990s. With wolves absent for near­ly a cen­tu­ry, elk had got­ten into the habit of relax­ing lazi­ly near streams like a herd of cows. The pres­ence of wolves kept elk on the move—which allows the stream-side wil­lows and veg­e­ta­tion to replen­ish itself, lead­ing to cool­er water and more trout. The wolves also kicked coy­otes off the top of the food chain, which allowed the pop­u­la­tion of ground squir­rels to rebound. More squir­rels meant more pine cones being moved around, which meant a greater regen­er­a­tion of pine forests from fire and insect infes­ta­tions. As a result, the parts of Yel­low­stone with wolves regen­er­at­ed far faster from the mas­sive fire of 1988 than the areas with­out wolves.

The Red-Backed Vole
A hum­ble crit­ter about four inch­es long, the red-backed vole lives almost entire­ly under­ground in the damp forests of the Pacif­ic North­west. Hang­ing out amidst the spongy soil and tree roots, its sole source of food is the fruit­ing body of a fun­gus that melds with tree roots to pull nitro­gen from the soil. The vole’s under­ground wan­der­ings spreads the fun­gus through­out the for­est. Since usable nitro­gen is a lim­it­ing fac­tor to plant growth, the vole is a key dis­trib­u­tor of a rare com­mod­i­ty, and is essen­tial to the giant trees of the north­west coast becom­ing so huge. They’re also the main prey source for a more famous crea­ture, the North­ern Spot­ted Owl, which is used as an indi­ca­tor of ancient for­est health because they depend on the voles in these old forests—but unlike voles, they live above ground and are eas­i­er to count.

Pacif­ic Salmon
Salmon are many things: an icon of the Pacif­ic North­west, a major sport­fish, an endan­gered species, the cen­ter of a fish­ing indus­try, and very tasty. They’re also proof that a fish can build…a for­est. When salmon migrate up to their birth streams and die, they bring with them a mas­sive amount of pro­tein and nitro­gen that dies and decays into the soil, stim­u­lat­ing plant growth (and even­tu­al­ly being drawn into the fun­gus that our friend the red-backed vole carts around under­ground). Where salmon runs are deplet­ed, plant growth is weak­er and forests regen­er­ate from dis­tur­bances slow­er than when runs are healthy. That’s why ecol­o­gists have begun “fish car­cass toss­ing” to replen­ish the nitro­gen sup­ply in river­side forests.

The Ghost Shrimp
Even more hum­ble than the vole, the Ghost Shrimp both lives under­ground and lacks the vole’s cute fur­ri­ness. They live in the mud of coastal salt marsh­es, where they dig bur­rows. They are con­stant­ly clean­ing out their bur­rows, which leads to a con­tin­u­ous redis­tri­b­u­tion of sed­i­ment. This con­tin­u­ous dig­ging of bur­rows pro­vides oth­er crit­ters a rent-free place to hide. The com­bi­na­tion of water flow­ing through their bur­rows and a rich array of crit­ters speeds the decom­po­si­tion of organ­ic mate­ri­als in estu­ar­ies, mak­ing them one of the most pro­duc­tive eco­log­i­cal zones on earth.

So next time you see one of these critters—a cute otter, a majes­tic wolf, or a tiny lit­tle vole you’ve nev­er heard of—tip your hat to them. They’re not just run­ning around mak­ing a liv­ing and avoid­ing preda­tors. They’re chang­ing the entire world around us.