17. Keystone Species and Biodiversity Flashcards
What is the Keystone Species?
- The keystone species could be any organism (i.e., a huge predator, an unassuming plant, or even bacteria and fungi), but without them the ecosystem may not survive or change drastically
- Overall, keystone species exert very strong control over environment of other species in a community, and changes in their numbers have many effects on food chains and webs
What is Biodiversity?
Biodiversity (or biological diversity) describes the variety and variability of all living organisms within a given ecological area
What is Species richness?
Species richness:
– Measure of the # of different types of species in an area
– A large number of different species in a habitat represents a higher species richness
What is Species evenness?
Species evenness:
– Measure of the relative abundance of each species in an area (i.e., number of each species)
– Describes how even the species are distributed in a particular ecological area
– More evenly represented species (evidenced by similar population sizes) illustrate a higher species evenness
What is the Simpson’s Reciprocal Index?
Simpson’s Reciprocal Index –
a measure of biodiversity that takes into account both species richness and species evenness
In regards to Simpson’s Reciprocal Index, what is a high index? What is a low index?
A higher index value corresponds to a greater degree of biodiversity (high richness and evenness) – suggests a stable site
A lower index value corresponds to a lesser degree of biodiversity (low richness and evenness)
Simpson’s Reciprocal Index Equation:
List Keystone Species: (6)
- Sea Otter
- Bumblebee
- Prairie Dogs
- Beavers
- Grey Wolves
- Saguaro Cactus
Why is the SEA OTTER a Keystone Species?
(3)
Otters feed extensively on sea-urchins, species that eat kelp, and when abundant, can decimate kelp beds
– As sea urchin density decreases from sea otter predation, so does the grazing pressure on kelp and as a result kelp forests flourish
- Removal of sea otters along the Pacific Coast caused major reductions in kelp, negatively affecting (i) many fish and invertebrates whose habitat includes kelp beds, as well as (ii) some species of crabs, snails, and geese that depend on kelp for food
- Re-introduction of sea otters allowed for predation on sea urchins to resume and restored the kelp communities (“kelp forests”)
Why is the BUMBLEBEE a Keystone Species?
(3)
- With the aid of other pollinators (some of which, like hummingbirds, are also keystone species), bees support the reproduction of as much as 90% of the world’s flowering plants
- They are keystone species in most terrestrial ecosystems, necessary not only for the reproduction of countless native wildflowers but also creating the seeds and fruits that feed wildlife such as songbirds and grizzly bears
- Without bees, many plant species would become extinct, as would the animals that feed on those plants – soon afterwards, carnivores are impacted as they would have nothing to eat
Why are PRAIRIE DOGS a Keystone Species?
(3)
- Residing in the grasslands of central and western North America, prairie dogs are a keystone species that supports many other species
- In addition to serving as a food source for coyotes, eagles, foxes, hawks, and black-footed ferrets, they maintain the health of arid grasslands by churning, aerating, and fertilizing soil as they create vast and intricate underground colonies
– The digging by prairie dogs allows vegetation to thrive
– This, in turn, supports a greater number of elk, bison, and other grazers.
- Furthermore, their burrows provide shelter for animals like rattlesnakes, burrowing owls, and jackrabbits
Why is the BEAVER a Keystone Species?
(4)
- Like prairie dogs, beavers are “ecosystem engineers” that dramatically reshape the physical environment around them
- Well-known for building lodges and dams – large structures in rivers and streams that can cause flooding and create new habitats
- Wetland habitats created from beaver flooding provide direct benefits to other organisms (including humans)
– These wetlands filter and purify water, refill aquifers, mitigate erosion, prevent droughts and control floods
– Wetlands are critical habitat for fish, birds, turtles, frogs, and ducks – some of these are in turn important food sources for many other species, including otters, foxes, and birds of prey - When beavers take down trees to eat from and build with, they open up the canopy of the forest
– More light penetrates the forest floor
– New plants and trees start to sprout almost immediately; and grow quickly with all the new sunlight and space
Why are GREY WOLVES a Keystone Species?
(5)
- Top-level predator (apex) whose presence has a ripple effect on the rest of its ecosystem
- Help keep deer and elk populations in check, preventing them from overgrazing on tree saplings (i.e., willow and aspen)
– This allows the development of saplings into large trees, whose root systems prevent riverbank erosion
– In addition, the trees provide habitats for other animals (such as beavers when it comes to dam building) - Wolves are a benefit to other predator populations – their uneaten food scraps help strengthen the food supply of other scavengers like bears, coyotes, and eagles
Why is the SAGUARO CACTUS a Keystone Species? (2)
- Native to the Sonoran Desert of the southwestern United States and northwestern Mexico – these tree-like cactus species can grow to be over 12 meters (40 feet) tall
- Provides critical nesting spots for birds like red-tailed hawks and woodpeckers (the latter of which peck new nest holes each year, leaving old holes for other birds)
- These cacti serve as an important source of sustenance, too – their blooming flowers feed bats, birds, and bees, while their fruit, which ripens when the desert is at its driest, is often the sole wet food source for myriad mammals, insects, and other species
