Despite its 1989 designation as a threatened species under
the federal Endangered Species Act, the desert tortoise,
Gopherus agassizii, has declined in numbers by ninety
percent since the 1980s. Although federal protection made
it illegal to harm desert tortoises or remove them from
the wild of the southwestern North American deserts, this
measure has been insufficient to reverse the species’
decline, and further intervention is required.
Recovery has been slow, partly due to the desert tortoise’s
low reproductive potential. Females breed only after
reaching full size at fifteen to twenty years of age, and
even then may only lay eggs when adequate forage is
available. Although the number of eggs in each clutch
varies, and each female might lay a few clutches in one
season, the average mature female produces only a few
eggs annually. From these precious eggs, hatchlings
emerge wearing soft shells that will harden slowly into
protective armor over the next five years. The vulnerable
young are entirely neglected by adult tortoises, and only
five percent ultimately reach adulthood.
Predators are blamed for most tortoise deaths; ravens,
specifically, are estimated to cause more than half of the
juvenile tortoise deaths in the Mojave Desert. Tortoise
eggs and juveniles, with their delicate shells, can fall prey
to many birds, mammals, and other reptiles. For protection
from predators, as well as from desert temperature
extremes, tortoises of all ages burrow into the earth.
However, if rabbits and rodents are scarce, larger
mammalian predators may dig tortoises out of their
burrows, devouring even mature tortoises despite their
hardened shells.
Even with current protections from human interference,
the desert tortoise faces a tough recovery, so additional
measures must be taken. First, the limited habitat of desert
tortoises, with soil suitable for their burrows, must be
protected from development. Next, urban expansion often
has the unintended effect of increasing raven populations,
so aggressive measures to control the birds are necessary
to increase desert tortoise hatchling survival rates. Finally,
released captive tortoises typically perish, and can pass
upper respiratory tract disease into the wild population
with devastating consequences, so continuing education
of pet tortoise owners is essential.
1. It can be inferred from the passage that the desert
tortoise mortality rate would be most likely to
decrease if which of the following were true?
· Desert tortoise burrows were cooler.
· Male and female tortoises mated more frequently.
· Adult tortoises provided better care for their young.
· Forage plants were abundant in the habitat of the
desert tortoise.
· Rabbits were abundant in the habitat of the desert
tortoise.
2. The passage mentions each of the following as
reasons that the desert tortoise is a threatened
species EXCEPT
· expansion of urban areas near the desert tortoise
habitat
· the low reproductive rate of desert tortoises
· desert temperature extremes
· predation by ravens
· the release of captive tortoises by pet owners
3. The primary intent of the passage is to do which of
the following?
· Describe the lifecycle of a species
· Advocate future actions
· Discuss a problem
· Evaluate past actions
· Criticize the government
4. Previous efforts to protect the desert tortoise are
regarded by the author with
· weary skepticism
· complete satisfaction
· implied opposition
· qualified approval
· overt disdain
the federal Endangered Species Act, the desert tortoise,
Gopherus agassizii, has declined in numbers by ninety
percent since the 1980s. Although federal protection made
it illegal to harm desert tortoises or remove them from
the wild of the southwestern North American deserts, this
measure has been insufficient to reverse the species’
decline, and further intervention is required.
Recovery has been slow, partly due to the desert tortoise’s
low reproductive potential. Females breed only after
reaching full size at fifteen to twenty years of age, and
even then may only lay eggs when adequate forage is
available. Although the number of eggs in each clutch
varies, and each female might lay a few clutches in one
season, the average mature female produces only a few
eggs annually. From these precious eggs, hatchlings
emerge wearing soft shells that will harden slowly into
protective armor over the next five years. The vulnerable
young are entirely neglected by adult tortoises, and only
five percent ultimately reach adulthood.
Predators are blamed for most tortoise deaths; ravens,
specifically, are estimated to cause more than half of the
juvenile tortoise deaths in the Mojave Desert. Tortoise
eggs and juveniles, with their delicate shells, can fall prey
to many birds, mammals, and other reptiles. For protection
from predators, as well as from desert temperature
extremes, tortoises of all ages burrow into the earth.
However, if rabbits and rodents are scarce, larger
mammalian predators may dig tortoises out of their
burrows, devouring even mature tortoises despite their
hardened shells.
Even with current protections from human interference,
the desert tortoise faces a tough recovery, so additional
measures must be taken. First, the limited habitat of desert
tortoises, with soil suitable for their burrows, must be
protected from development. Next, urban expansion often
has the unintended effect of increasing raven populations,
so aggressive measures to control the birds are necessary
to increase desert tortoise hatchling survival rates. Finally,
released captive tortoises typically perish, and can pass
upper respiratory tract disease into the wild population
with devastating consequences, so continuing education
of pet tortoise owners is essential.
1. It can be inferred from the passage that the desert
tortoise mortality rate would be most likely to
decrease if which of the following were true?
· Desert tortoise burrows were cooler.
· Male and female tortoises mated more frequently.
· Adult tortoises provided better care for their young.
· Forage plants were abundant in the habitat of the
desert tortoise.
· Rabbits were abundant in the habitat of the desert
tortoise.
2. The passage mentions each of the following as
reasons that the desert tortoise is a threatened
species EXCEPT
· expansion of urban areas near the desert tortoise
habitat
· the low reproductive rate of desert tortoises
· desert temperature extremes
· predation by ravens
· the release of captive tortoises by pet owners
3. The primary intent of the passage is to do which of
the following?
· Describe the lifecycle of a species
· Advocate future actions
· Discuss a problem
· Evaluate past actions
· Criticize the government
4. Previous efforts to protect the desert tortoise are
regarded by the author with
· weary skepticism
· complete satisfaction
· implied opposition
· qualified approval
· overt disdain