How many species are there? Species richness the total number
of species in an area. 5-10 million is best guess, but may be
anywhere from 3- 100 million.
Slide 4
Biogeographic Patterns Latitudinal Gradient The number of
species is greatest near the equator and decreases as you move
toward the poles.
Slide 5
Latitudinal Gradient Raises these Questions: What determines
how many species live in a particular area? Why do some regions
have more species than others? Is there any limit to the number of
species Earth can support?
Slide 6
Biogeographic Realms & Regions Different portions of the
globe frequently have unique biotas. A rainforest in South America
has species more closely related to those found in South American
prairies than to rainforest species in Africa. This became known as
Buffon's Law.
Slide 7
Biogeographic Realms & Regions What determines which
species are found in a particular region? Why are some species
widely distributed while others have more restricted ranges? How
does a species' evolutionary history affect its current
distribution?
Slide 8
Biogeographers consider two distinct perspectives to answer all
these questions: The first is an ecological perspective, concerned
with how short-term interactions among organisms and the physical
environment affect a species' current distribution. The second is
an historic perspective that focuses on how processes like
speciation, extinction and dispersal af fect taxa and biotas.
Slide 9
Sampling Species Richness How do we determine the total number
of species in the area. Sampling effort Species accumulation
curve
Slide 10
Why do some areas have greater species diversity? Hypothesis #1
The number of species on any wall is determined by the number of of
species in the regional species pool. Each time space in a site
opens up, it may be settled by any colonist arriving from the
regional species pool, the size of which is determined by rates of
speciation and extinction.
Slide 11
Why do some areas have greater species diversity? Hypothesis #2
The number of species on any wall is determined by local species
interactions. Competition for space and other resources,
predator/prey dynamics, etc., drive diversity by determining which
species can survive at any given site and whether or not a new
species can successfully colonize it.
Slide 12
Hypotheses lead to Predictions In contrast, if species
interactions limit the species that can live in a particular place,
then as local species richness increases, species interactions will
become more and more intense until, eventually, new species are
unable to colonize the site. Strong interspecific interactions will
place an upper limit on alpha diversity, regardless of the size of
the regional species pool.
Slide 13
Species Turnover If you compared two communities within a
region, you might find they have few species in common. This
turnover in species from one site to the next is also a form of
diversity. Biogeographers describe this as beta diversity.
Slide 14
Generalists vs Specialists Generalist species that can reach
and occupy just about any habitat type will see any region as one
large continuous area full of suitable habitat. In contrast,
specialist species that have very narrow niches will see the same
area as divided into many distinct habitats, only some of which
they can occupy
Slide 15
Biogeography and Conservation Biology One practical reason to
study Earth's biodiversity is so we can judge whether there is
really an extinction crisis happening now.
Slide 16
Human-Related Causes of Extinction Hunting, introduced species,
and anthropogenic habitat degradation are big threats to diversity
now, just as they were in the past, although technological advances
have enabled people to clear forests more quickly and hunt animals
more efficiently than their prehistoric ancestors.
Slide 17
Why Protect Biodiversity? Protect the "genetic library" of
natural ecosystems. Earth's biodiversity has already provided
humanity with food, medicines, and many other resources.
Slide 18
Why Protect Biodiversity? Ecosystems provide a broad set of
services that we rely on for our welfare. These ecosystem services
include things like climate regulation, water purification, flood
control, crop pollination, and soil generation and
maintenance.
Slide 19
Why Protect Biodiversity? People have an aesthetic and ethical
obligation to protect our planet and the only other living species
known in the universeeven if only so future generations can marvel
at the wonderful diversity of life on Earth.
Slide 20
Ecological Biogeography
Slide 21
Species-Area Curves Bigger islands tend to have more species.
Easiest to see pattern if data is log-transformed.
Slide 22
Islands From an organism's perspective, an island is simply an
area of suitable habitat surrounded by an inhospitable landscape
matrix. With this definition there are any number of habitats that
could be islands, such as caves, desert oases, and the cool
habitats of mountain tops.
Slide 23
Island Biogeography An island's species richness is determined
by three distinct processes: Immigration Extinction Evolution
Slide 24
McArthur & Wilson Equilibrium theory of island
biogeography, focused on islands that varied in size and distance
from a mainland. They restricted their analysis to ecological time
scales, ignoring evolution.
Slide 25
Immigration Rate Immigration rate is affected by: Size of the
island Distance from the mainland
Slide 26
Extinction Rate The extinction rate will be affected by the
availability of resources. If more species than can be supported by
the available resources have immigrated to the island, there will
be a high extinction rate.
Slide 27
Equilibrium Theory of Island Biogeography MacArthur and Wilson
plotted an island's immigration and extinction rate curves on the
same set of axes and made two important predictions about an
island's biota.
Slide 28
Equilibrium Theory of Island Biogeography The intersection of
the two curves, which occurs when immigration rate equals
extinction rate, predicts the equilibrium number of species, S*.
When the number of species on an island is greater than S*, the
extinction rate exceeds the immigration rate, and the number of
species on the island will decrease. Conversely, when the number of
species is smaller than S*, immigration exceeds extinction and the
number of species will increase.
Slide 29
Equilibrium Theory of Island Biogeography The intersection of
the two curves also predicts the rate at which new species replace
extinct species, reflecting the dynamic nature of equilibrium on
the island. There is one theoretical value of S*, but the
composition of S* is always changing. It changes at a rate that
MacArthur and Wilson called the equilibrium turnover rate,
symbolized as T*.
Slide 30
Support for Turnover Natural experiments supported the concept
that species turnover. Krakatau Channel Islands Manipulative field
experiments also supported turnover. Florida Keys mangrove
islands
Slide 31
Mangrove Experiments Showed the affects of size and distance
from the mainland.
Slide 32
Complicating Factors Many communities seldom, if ever, attain
an equilibrium number of species. Both natural and anthropogenic
disturbances like hurricanes, volcanic eruptions, and clear-cutting
can remove species and open up habitat. Evolution can add species
to either the island community or to the mainland species
pool.
Slide 33
Complicating Factors Islands are not homogenous patches sitting
within a featureless seascape. Both islands and their surroundings
can have complex environments which can alter immigration and
extinction rates
Slide 34
Complicating Factors Species are not interchangeable. Whether
or not a species successfully colonizes an island or later goes
extinct is affected by its inherent biology and by interactions
with other members of the community.
Slide 35
Dispersal For a species to colonize an island, individuals of
that species must move there. Movement of individuals between
different islands or other patches of good habitat is known as
dispersal. Barriers to dispersal prevent organisms from
immigrating.
Slide 36
Types of Barriers Types of barriers that species might need to
cross in order to successfully move from one patch to another:
Corridors are routes through a landscape that all species can
cross. Filters are routes that only some species can cross.
Sweepstakes routes are those that are nearly impossible to cross
except during rare and unpredictable circumstances.
Slide 37
Crossing Barriers Biogeographers recognize three means by which
a barrier might be crossed: Jump dispersal occurs when an organism
leaps a barrier in a single bound. Diffusion occurs when organisms
slowly percolate through a relatively hospitable matrix. Secular
migration occurs when populations move so slowly from one area to
another that they evolve en route.
Slide 38
Dispersal Example Some 40-45 million years ago, the ancestor
species to camels and llamas (family Camelidae) originated in North
America. About 3 million years ago some of these animals migrated
west across the land bridge from Alaska to Siberia, and from there
dispersed across Asia and into Africa (see the arrows on the
right). When South America crashed into North America at Panama,
other individuals migrated south along the newly formed corridor of
land. In this way, the original ancestor species in North America
dispersed to four different continents.
Slide 39
Species-Area Curves Both island and mainland species- area
curves tend to show the same general pattern. Larger areas contain
more species.
Slide 40
Species-Habitat Diversity Hypothesis As you expand sampling
area, you will encounter different habitats, and thus different
sets of species. This is known as the species-habitat diversity
hypothesis.
Slide 41
Island Biogeography & Conservation Biology An early
question conservation biologists asked was: Given the ability to
set aside a certain amount of land as a reserve, is it better to
target single large pieces of land or several small pieces? Because
extinction rates are lower in larger areas, some ecologists argued
that making the largest reserve possible would keep the most
species from going extinct. Others argued that several smaller
reserves might capture more habitat diversity, as well as protect
against major disturbances (e.g., what if a fire burned down all of
a single large reserve?).
Slide 42
Historical Biogeography
Slide 43
Evidence of Major Changes Fossils of aquatic animals, such as
large sharks, in Kansas indicate that the Earth has changed
dramatically over time.
Slide 44
Plate Tectonics Such huge changes in geography happen because
Earth's continents slide across the surface of the planet in a
process known as plate tectonics. https://youtu.be/Cm5giPd5Uro
Slide 45
Realms & Regions Earth's terrestrial biota can be divided
into 12 biogeographic realms that reflect the different
evolutionary histories of land masses on different tectonic
plates.
Slide 46
Allopatric Speciation Allopatric speciation begins when
populations of the same species become geographically isolated.
Over time, natural selection and drift cause them to diverge
evolutionarily until they are distinct, reproductively isolated
species. This may occur as a result of two distinct processes: A
vicariance event occurs when a population is physically split by
geologic or geomorphic processes. A founder event occurs when a new
population is founded by a small number of individuals dispersing
from their ancestral range.
Slide 47
A Brief History of Frogs If you could time-travel back onto the
Madagascar-India-Seychelles fragment 100 million years ago, you
would see frogs that remind you of today's American bullfrog and
leopard frog species. What frog history led them from a single
species on a fragment of land off Africa to a nearly worldwide
distribution today?
Slide 48
A Brief History of Frogs The breakup of the southern continent,
Gondwana, created smaller, isolated populations on the new land
masses. As the land masses separated, ocean water filled the gap.
Animals like frogs could not cross the gaps. This is an example of
vicariance.
Slide 49
A Brief History of Frogs According to the model of allopatric
speciation, once two populations are physically isolated, the
evolutionary processes of mutation, natural selection, and genetic
drift would cause mating behavior, feeding strategies, and habitat
use to become different between the populations. Over long enough
time spans, new, reproductively isolated species were likely to
evolve.
Slide 50
Jump Dispersal Geologically-caused vicariance events are one
way for populations to become isolated. A different way is through
jump dispersal. If individuals from the one population cross a
barrier (such as a stretch of ocean) to a new, unoccupied habitat,
the new population may be isolated enough to eventually evolve into
a new species. Founder Event
Slide 51
A Brief History of Frogs We can make predictions about the
pattern of speciation we would expect from dispersal
Slide 52
Sympatric Speciation Sympatric speciation occurs when a
population splits into two and eventually speciates without a
physical separation.
Slide 53
The Great American Biotic Interchange Approximately 3 million
years ago the Isthmus of Panama emerged from the sea, connecting
North and South America. Route for mammals to cross from one
continent to another.
Slide 54
Human Accelerated Dispersal Although dispersal and colonization
of new habitats is a fundamental biogeographic process, humans have
altered dispersal rates for many species. Intentionally and
accidentally, people bring species with them as they move from
place to place.
Slide 55
Introduced Species - Impacts Introduced species often lead to
extinction of native species and loss of biodiversity. Because many
of the same species are introduced over and over again, many areas
of Earth are losing their distinctive nature.
Slide 56
Latitudinal Gradients Latitudinal gradients are perhaps the
best- known biogeographical pattern. Species diversity tends to be
high near the equator and lower near the poles for many taxa. These
patterns are well-correlated with a number of climatic variables
but are incompletely understood.
Slide 57
Biodiversity Hotspots & Conservation Conservation
biologists have attempted to identify hotspots that contain a large
number of endemic species that are threatened by human activities.
Focusing conservation activities on these hotspots may be an
effective use of limited conservation resources.
Slide 58
Global Patterns in Physical Conditions
Slide 59
Climate predicts not only the number of species likely to occur
in a place, but also the physical appearance of those species.
Slide 60
Differential Energy Input from the Sun Because the Earth is
round, the intensity of solar radiation is lower in the poles than
near the Equator.
Slide 61
The Tilt and Orbit of the Earth Creates Seasons The tilt of the
Earth's axis relative to its orbital plane creates
seasonality.
Slide 62
Atmospheric Circulation Differential heating from the Sun
across the globe creates air and water currents, such as Hadley
cells.
Slide 63
Bands of Wet and Dry Large-scale air circulation patterns tend
to create a band of wet areas near the Equator and deserts to the
north and south of the Equator.
Slide 64
Terrestrial Biomes Differences in climate and geography give
rise to a variety of biomes around the world. These patterns
determine a region's climate and, to a large degree, what species
can thrive there.
Slide 65
Temperate Deciduous Forest Temperate deciduous forests receive
rain year-round. Cold winters and hot, humid summers. Animals may
migrate, hibernate, or survive on scarce available food or stored
fat through the winter.
Slide 66
Coniferous Forest Coniferous forests, or taiga, are common in
the northern hemisphere. Evergreens dominant Colder, less rain than
temperate forests.
Slide 67
Coniferous Forest Mammals that inhabit coniferous forests
include deer, moose, elk, snowshoe hares, wolves, foxes, lynxes,
weasels, bears. Adapted for long, snowy winters.
Slide 68
Tropical Forest Tropical rain forests receive lots of rain and
are generally warm year-round. Stratified Diverse
Slide 69
Tropical Forest Canopy insectivorous birds and bats fly above
the canopy. Fruit bats, canopy birds, and mammals live in the
canopy eating leaves & fruit. Middle zones are home to arboreal
mammals (monkeys, sloths), birds, bats, insects, amphibians.
Climbing animals move along the tree trunks feeding at all levels.
Ground level contains larger mammals (capybara, paca, agouti, pigs)
as well as a variety of reptiles and amphibians.
Slide 70
Tropical Forest Nutrients in a tropical forest are tied up in
living organisms. Soil is poor. Slash and burn agriculture involves
removing vegetation to grow crops but the soil is so poor that the
fields must be moved often.
Slide 71
Grassland Temperate grasslands receive seasonal precipitation
and have cold winters and hot summers. Prairie
Slide 72
Grassland Grasses and herds of large grazing mammals are
dominant. Jackrabbits, prairie dogs, and ground squirrels are
common. Predators include coyotes, cougars, bobcats, raptors,
badgers, and ferrets.
Slide 73
Grassland Savannas are tropical grasslands with seasonal
rainfall.
Slide 74
Grassland Chaparral receives highly seasonal rainfall. Shrubs
and small trees are common. Adaptations to fire.
Slide 75
Tundra Tundra has a permanently frozen layer of soil called
permafrost that prevents water infiltration. Very cold, short
growing season. Little rain
Slide 76
Tundra Tundra is often covered with bogs, marshes, or ponds.
Grasses, sedges, and lichens may be common. Lemmings, caribou,
musk-oxen, arctic foxes, arctic hares, ptarmigans and other
migratory birds.
Slide 77
Desert Deserts have very low precipitation less than 30 cm/yr.
Variable temperatures. Animals often nocturnal and live in burrows.
Reptiles and small mammals are common.
Slide 78
Establishing Conservation Priorities Understanding the
distribution of the Earth's flora and fauna across the globe can
greatly assist conservation efforts, but naming and mapping biomes
and ecoregions is not enough. To make the best-informed decisions
possible, conservation biologists want to know more about these
places, including the threats that they face and the species they
contain.