Macroevolution Flashcards
the origin and extinction of new taxonomic groups.
It can happen gradually, or slowly.
Macroevolution
The two major processes of macroevolution
Speciation
Extinction
A modern understanding of speciation begins 100 years after Darwin, when Ernst Mayr, and others, developed a scientific theory of speciation based upon
Extinction took even longer
Genetic and Ecological Processes
Species are groups of actually or potentially interbreeding individuals that can mate and produce fertile offspring
A species is the smallest set of organisms that share a common ancestor, and can be distinguished from other such sets
Biological Species Concept
Phylogenetic Species Concept
Species are collections of living organisms that have certain morphological and biochemical traits in common.
Morphological Species Concept
This idea was promoted by Ernst Mayr, an evolutionary biologist who worked on birds.
It is excellent, conceptually, because it defines species objectively, based upon the capabilities of the organisms in question.
BIiological Species Concept
In principle, this applies to most species, but in many cases, it is simply impossible to test whether two species have the potential to interbreed.
Fossil species, species which do not reproduce in the lab or zoo (the vast majority), and asexual species are sticky issues.
Biological species concept
This is what most taxonomists actually use to classify specimens and describe species.
It is expedient-it can be applied to dead specimens, and even to fossils.
Morphological Species Concept
It has many disadvantages.
It is subjective.
Cryptic species, which look identical to humans but are in fact reproductively isolated, are problematic.
Species with morphological variation, and complex life histories, pose problems.
Morphological Species Concept
This concept emphasizes the species as a lineage on the tree of life.
It is, at least in theory, objective, because it defines lineages as the smallest set of organisms that share a common ancestor-though in practice, that common ancestor is always dead, and its existence must be inferred.
Phylogenetic Species Concept
the origin of new species. With extinction, it is one of two keystone processes of macroevolution
It is one of two cornerstone processes of macroevolution.
It takes _____ for species to originate
Speciation
Reproductive Isolation
If this reproductive isolation continues long enough, speciation occurs. One, or several, new species originate from isolated populations of the parent species.
As we shall see, this is frequently the result of a geographic barrier, although it may be the result of a chromosomal change or habitat preference.
This type of species live in the same place. Without some mechanism preventing allele and gene exchange among sympatric species, distinct species would be impossible.
Sympatric Species
Instead, we would see a continuum of variation from one form of life to another, and many forms of life would not be possible, because interbreeding with different forms would produce non-viable combinations of traits
Barriers to allele flow are called …
They allow sympatric species to exist and to maintain distinct sets of characters and adaptations.
Isolation Mechanisms
Without isolation mechanisms, closely related species would hybridize: allele flow and recombination would eventually transform them into a single, polymorphic species.
Isolation mechanisms are responsible for the origin of species, and they maintain the integrity of species
Isolation mechanisms prevent mating, so that gametes of sympatric species never form hybrid zygotes.
Prezygotic Isolation mechanisms
Isolation mechanisms that act after a mating has occurred, to prevent fertilization or to prevent potential hybrids from passing on their genes.
Postzygotic Isolation Mechanisms
The 5 prezygotic isolation mechanisms
Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation Gametes Die
occurs because sympatric species never meet due to differences in their habitat preference.
Habitat Isolation
What type of isolation?
Sympatric species of spadefoot toads (Scaphiopus) seldom meet because they prefer different soil types.
Habitat Isolation
Type of isolation?
Many species of closely-related parasites, such as bird lice, never meet because they live and mate on different hosts.
Habitat Isolation
Isolation that occurs because species mate at different times
Temporal Isolation
Type of isolation
The American Toad (Bufo americanus) and the Fowler’s Toad (Bufo fowleri) have been mated in laboratory settings, but mating does not happen in the wild because the American Toad mates early in the summer, and the Fowler’s Toad mates in late summer.
Temporal Isolation
isolation mechanisms that include differences in courtship behavior, differences in chemical signals or vocalizations, and differences in color or morphology that allow individuals to recognize their own species.
They are a very common mechanism keeping closely-related sympatric animals from interbreeding
Behavioral/Ethological Isolation
Birds are very visually-oriented creatures, with extensive behavioral repertoires. Visual recognition is thought to play a key role in mate recognition for most species.
Gulls normally mate only with their own species.
NOTE. The point of this experiment is to demonstrate the existence of an isolation mechanism by artificially removing it
Artificial hybridization can be induced by cross-fostering herring gulls and lesser black-backed gulls. Members of each species “imprint” on archetypes of their own species as juveniles. If eggs are switched, they imprint on the wrong species, and hybridize. Thus, the isolation mechanism is behavioral.
occurs because the sexual organs of closely-related sympatric species are incompatible: they do not fit together.
This is thought to be an important isolation mechanism in arthropods, particularly insects and millipedes.
Mechanical Isolation
The adeagus (closest thing there is to a penis) of various Drosophila species is an example of
Mechanical Isolation
Gametes are frequently very specialized cells, which can only perform well in the reproductive tract of the opposite sex of the same species.
In many angiosperms, for instance, pollen transferred to the stigma of another species will not germinate, or if they do, will not form a pollen tube.
Gametic Mortality
Some species that do not ordinarily interbreed occasionally do so. Frequently, the progeny of these interspecific matings die at some point during their development.
Hybrid Inviability
Ex: Hybrids between the frogs Rana pipiens and Rana sylvatica do not survive more than a day or so
Hybrid Inviability
occurs when the hybrid of an interspecific mating is unable to reproduce.
Examples: Mules are the hybrid of a horse and a donkey, they do not form normal sperm
Hybrid Sterility
Hybrids between Drosophila melanogaster and D. pseudoobscura exhibit what type of post-zygotic isolation?
Hybrid sterility
If interspecific hybrids do survive, they often have very low fitness, this effectively keeps them from spreading genes from one of their parent species to the other parent species
Low Hybrid Fitness
Dog-Wolf hybrids are perfectly viable, but they are considered to be unsuitable pets in most areas.
Wild wolf populations do not accept hybrids, they are killed on sight.
Low Hybrid Fitness
Speciation that involves a geographic barrier
Allopatric Speciation
Speciation that does not involve a geographic barrier
Sympatric Speciation
involves a geographic barrier that physically isolates populations of a species and blocks gene flow.
Once isolated, allopatric populations (living in different places) accumulate genetic differences due to
Natural Selection, Sexual Selection, Genetic Drift, New Mutations
If the Geographic Barrier is Removed, the Two Species May:
1) meld together by allele flow and recombination to once again form a single species.
2) remain reproductively isolated
The new species that results when geographic barriers are removed and they meld together by allele flow and recombination
Incipient Species
Its fate depends upon whether isolation mechanisms have evolved during the period of isolation
Incipient Species
These isolation mechanisms may be premating or postmating.
Premating isolation mechanisms may evolve in incipient species that have postmating isolation, to reduce the probability of incorrect matings and the subsequent loss of fitness.
!
Two closely-related species of antelope squirrels live on opposite sides of the grand canyon. On the South rim is
on the North rim is Ammospermophlus leucurus
Ammospermophilus harrisi
Have species(Birds) that can cross the grand canyon diverged into different species on opposite sides?
No.
a black bird with a crest of feathers, it is highly variable in behavior and appearance throughout its range.
Each semi-isolated population has its own appearance.
A “double” invasion probably occurred in Tasmania over the course of the past few thousand years.
The Drongo
This species is widespread on the Australian continent. Tasmania has a slightly differentiated population of this bird.
Acanthiza pusilla
Another, reproductively isolated species, that is even more differentiated from Australian Drongos in appearance and morphology also inhabits Tasmania
A. ewingi
During the last ice age, when sea level was lower, Tasmania was part of an island, this is probably when the ancestors of A. ewingi invaded the island. Eventually they evolved reproductive isolation from their Australian counterparts.
When A. pusilla re-invaded the island more recently, the two species were able to co-exist because they are reproductively isolated.
Nobody knows for sure how long allopatric speciation takes, and it depends upon the group.
McCune and Lovejoy, based on a study of reproductive isolation in 40 pairs of allopatric fishes which were each other’s closest relative, estimated that, for fishes, it takes between
.8 and 2.4 million years for reproductive isolation to evolve.
Central America has only been an effective reproductive barrier to marine creatures for 3 million years. In that time, pairs of species of _______ have evolved on opposite sides of the isthmus
Snapping Shrimp
Hurt and Hedrick conducted interesting studies of incipient allopatric speciation in the Sonoran topminnows
Based on molecular evidence, these two species/subspecies have been isolated for between one and two million years in different river drainages in Arizona
Poeciliopsis sonorensis and Poeciliopsis occidentalis
Hurt and Hendrick found that males of each species prefer to mate with females of their own species, but given no choice, they will hybridize, rather than not mate.
Poeciliopsis sonorensis and Poeciliopsis occidentalis
What type of fitness did the hybrids of Poeciliopsis sonorensis and Poeciliopsis occidentalis have, especially when a hybrid was crossed with an original species?
Reduced hybrids
For this species, hybrids demonstrated brood sizes that were smaller, and there was an unusual, male-biased sex ratio for these crosses. Particularly occurred when a hybrid was crossed with an original species
Poeciliopsis sonorensis and Poeciliopsis occidentalis
This phenomenon-where the products of matings between the original species and hybrids with another species have especially low fitness, is called
It is a relatively common phenomenon in poztzygotic isolation scenarios
Hybrid breakdown
Are Poeciliopsis sonorensis and Poeciliopsis occidentalis separate species?
Clearly, the answer is subjective. In this case, if the populations were to mix together, the process of reinforcement would probably complete the job….so probably yes.
natural selection on females of incipient species pairs in cases where there are postzygotic isolating mechanisms, to avoid mating with males of the wrong species.
Any trait that causes them to avoid mating with the wrong species becomes common, because the cost of producing unfit offspring is avoided
Reinforcement
It is not usually observed in males, for the reason that females generally invest more in any given reproductive effort and have more to loose.
Reinforcement
Example-Coyne and Orr documented that Drosophila species pairs, such as _____ and ________ avoid interspecific matings, when they are captured from the parts of their range where these species overlap, but they do not avoid hybridization if they are captured from the parts of their range where there is no overlap between species.
D. pseudoobscura and D. persimilis
speciation that results from intrinsic factors, such as chromosomal changes and nonrandom mating.
Species become genetically isolated even though their ranges overlap
Sympatric Speciation
Name the mechanisms of sympatric speciation (2)
Polyploidy
Nonrandom Mating
Disorders of meiosis cause the accidental formation of gametes that are 2N rather than N. Self-fertilization, or any other union of two of these 2N gametes produces a zygote that is 4N
Poloyploidy
The chromosome number has doubled, instantaneously producing a potential new species.
This process is called
autopolyploidy
Gametes of two species meet and form a hybrid.
Usually the hybrid is sterile, but sometimes it is not.
Interspecific Hybridization
What is produced from interspecific Hybridization, which is usually infertile (the chromosomes can not pair during meiosis), but may reproduce asexually?
If the chromosomes double by a disorder of mitosis, and these cells go on to form germ-line tissue, it produces a potentially sexual species.
Allopolyploid
These mechanisms are probably common in plants, but rare or absent in animals.
Why?
Interspecific Hybridiztion, Allopolyploidy
Plants are frequently capable of self-fertilization, and some can survive with double the normal number of chromosomes, and most can propogate asexually.
Plants have no real germ line-somatic tissue, can give rise to meiotic tissue under a variety of circumstances-thus, an asexual species is likely to have individuals that have spontaneously doubled their chromosome number, and are forming gametes.
!
Wheat is doubly autopolyploid, the product of an interspecific hybridization, then a doubling of chromosomes, then another interspecific hybridization, then another doubling of chromosomes, to produce a fertile hexaploid.
Yellow bananas are a sterile allopolyploid, the product of two interspecific hybridization events.
! (look at diagram for wheat)
Many species of parasites mate on or nearby the host. A shift to a new species of host therefore reproductively isolates the parasites exploiting the different species of hosts.
Host Shift (Nonrandom Mating)
The best studied example of host shift occurs in the
apple maggot
Apple trees are not native to the US, they were introduced here in the nineteenth century.
Following their introduction, the hawthorn maggot began to feed on apples.
The flies cue in to the smell of their original host, so apple and hawthorn maggots are now reproductively isolated: and considered to be different species.
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Speciation is not always clear-cut, there are many examples of SOME populations being reproductively isolated, while OTHERS are able to interbreed. This is sometimes called
Parapatry
A well known example involves California garter snakes, Thamnophilus sp..
Each population of land snakes is able to interbreed with the populations closest to it, but not with more distant populations. In some cases, however, a distant population has come back around to encounter a distantly related population. In these cases, they do not interbreed.
Parapatry
A similar relationship exists for water populations. Some water snakes can even interbreed with the local land snakes
Parapatry
A “family tree” describing how species are related. The branching pattern of different groups of organisms is caused by repeated cladogenesis.
Phylogeny
is the study of phylogeny
Systematics
Is the process of describing and naming organisms. Our modern process of taxonomy is based on phylogeny, so an understanding of phylogenetic relationships-names reflect relatedness
Taxonomy
Every species has a place in the taxonomic hierarchy
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It is worth noting that systemetists form new rankings, such as infraorder, subphylum, etc., whenever they need to.
A more modern approach is to define groups on the tree of life based upon branching points.
This avoids the confusion of exactly what constitutes an order, etc.
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the origin of lineages, is the formation of a new branch on the tree of life. Speciation is the mechanism for it
Cladogenesis
promotes biological diversity by increasing the number of species
Cladogenesis
Extinctions pare down the number of species present on the planet, and thus, a lineage, such as mammals, with thousands of species, originally started as a single species.
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The branching pattern that gave rise to a group of taxa can be inferred from a variety of types of evidence.
These include:
- Morphological, biochemical, behavioral, and genetic features
- DNA sequence information
- The fossil record
- Biogeography
Shared morphological, biochemical, genetic, or behavioral characters that were passed down from a common ancestor are called
The most reliable in constructing a phylogeny for a group of organisms.
Homologies
A character state is _ in two species when it is inherited by both from a common ancestor.
Homologous
infers the pattern of phylogeny based on homologies. Groups are constructed based on shared characteristics inherited from a common ancestor, that no other group has.
The most widely accepted school of systematics today
Cladistics
For any group of taxa, a pattern of loss and acquisition of characters, and the subsequent passing-down of these traits to descendent species, can be mapped on a tree called a
Cladogram
The cladogram with the fewest number of transitions and reversals (parsimony), or
the one with the most likely series of transitions, is chosen as the best-supported phylogeny.
Parsimony
Maximum Likelihood
An evolutionary novelty for a group
An evolutionarily primitive state
Apomorphy
Pleisomorphy
a novel (derived) trait that a group has inherited because the common ancestor of that group had a novel characteristic and passed it on
Synapomorphy
an evolutionarily primitive trait that a group has inherited because the common ancestor of that group had inherited the primitive condition, unchanged, from an earlier group.
Synplesiomorphy
Note that these terms are relative-a synplesiomorphy for one group may be a synapomorphy from the larger group it came from.
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The wings of bees of the families andrenidae and Halictidae have basal veins, it is straight in adrenidae and curved in halictidae. It is a chief distinguishing feature between them that has remained constant during the long evolution o these groups. What is this an example of?
Synapomorphy
If a character has evolved more than once, if possessed by two species but not present in the common ancestor, it is called a
Homoplasy
One form of homoplasy that is quite common because different species are often subject to similar selective pressures.
Convergent Evolution
Homoplasy, when mistaken for homology, can obscure the pattern of evolutionary history.
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The labrum/food channel etc. of flies is an example of
Homoplasy NOT homology
A major force in macroevolution
Extinction
Species do not last forever…the mean expected lifespan of a marine bivalve is about
and the mean expected lifespan of a terrestrial mammal might be about a tenth that
14 million
As some species originate, they inevitably drive other species
Extinct
Extinctions pave the way for….
Speciation
a wave of speciation that occurs as a new habitat is colonized by a lineage, or in the wake of the extinctIon of another lineage.
Adaptive Radiation
An adaptive radiation of mammals followed the extinction of the dinosaurs.
An adaptive radiation of dinosaurs followed the extinction of the land crocodiles and mammal-like reptiles that preceded them.
!!
At all times in history, groups of organisms have a
Background Extinction Rate
Extinction rates are much higher than background rates for a short period of time, the history of life on Earth is riddled with these periods
Mass-Extinctions
5 Extinctions over the last 500 million years
1) The Late Devonian
2) Mid-Ordovician
3) Permian-Triassic
4) Late Triassic
5) Cretaceous-Paleogene.`
One of the best-understood mass-extinctions occurred at the end of the Mesozoic era, at the boundary between the Cretaceous Period and the Neogene period.
Every species of non-avian dinosaur was driven extinct, as well as pterosaurs, mosasaurs, plesiosaurs, the ammonoid and belemnoid molluscs, rudist bivalves, and quite a few other taxa as well.
The Cretaceous-Paleogene Mass Extinction
What percent of species was eliminated over an interval of 1,000 years during the Cretaceous-Paleogene Mass Extinction
50%
The scientific consensus, at the moment, is that one or several impact events are responsible for the extinction-though a severe marine regression at the time, and climate change induced by a period of intense vulcanism, may have played a role, rendering the biosphere much more susceptible to mass extinctions resulting from an impact.
The Cretaceous-Paleogene Mass Extinction
Since the development of agriculture, 10,000 years ago, humans have modified an increasing proportion of the Earth’s resources for our own purposes.
Humans impact has caused extinction rates to be 10 to 1000 times greater than any time in the last 100,000 years.
!
For example-one estimate for the recent background extinction rate for birds is one species extinction per
400 years
If only the background extinction rate affected the number of bird species, no more than a couple of extinctions should have occurred in the past 800 years.
Scientists estimate that the actual loss during this time period lies somewhere between
200 and 2,000
We have set in motion a mass extinction, one of the largest, that will not culminate until thousands of years from now.
The human population passed __ billion in the year 2012, and is growing at a rate of almost ___ per year (down from a maximum of over 2% per year).
7 billion
1.1%
Worldwide, more than __% of all land area is used for farms or permanent pastures. Much of the rest is grazed or logged on a regular basis.
35%
From ___ to ____& of Global Net Primary Productivity now goes to serve human needs
35-45%
In aquatic ecosystems as well, an increasing amount of productivity is harvested by humans. Nearly every major fishery in the Northern Hemisphere has showed strain from overharvesting, and many have collapsed.
!
The 4 Major Sources of Anthropogenic Extinction
Habitat Destruction and Habitat Fragmentation
Habitat Change and Disruption of Ecosystem Processes
Introduction of Exotics
Overexploitation
Most of the grasslands and forests of the Northern Hemisphere were destroyed by the end of the nineteenth century.
Habitat Destruction and Fragmentation
The grasslands of the southern hemisphere are now vanishing, and tropical forests are disappearing at a rate of about ___% per year
2%
This type of destruction has become the norm for most biological communities, as the human population expands our economic needs require resources from more and more land.
Habitat Destruction and Fragmentation
The remaining habitat is often broken into many small fragments, which are separated by large areas of land under cultivation or other human uses, effectively reducing a single “continent” into many “islands”.
Habitat Destruction and Habitat Fragmentation
Essentially, every habitat fragment becomes a biological “island” (analogous to continental shelf islands, rather than the oceanic kind).
As in the Mac Arthur Wilson model (see your textbook), the smaller the island, the ______ (larger/smaller) the population of any given species it can support
Smaller
Small populations are at much greater risk of extinction due to random events, such as weather, disasters, and natural fluctuations in their population.
Fragmented Habitats Support Smaller Populations
Additionally, smaller populations support less ____________, which could lead to the fixation of harmful alleles and the ultimate extinction of the population (for very small fragments), or simply inhibit their ability to evolve in response to changing conditions
Genetic Variation
Fire, certain types of grazing, and other forces fundamentally important to the ecology of organisms, are altered when a habitat is broken into fragments.
Fragmented Habitats Frequently Lack Critical Ecosystem Processes
For instance, places where human habitation borders nature preserves frequently have weedy plants, fire is controlled, domestic cats and dogs escape and prey on native wildlife, and human noise and activity disturb the behavior of certain animals.
For certain species, this can be critical to their ability to survive
Edge Effects
The edge habitats have different effects on different species.
Some large mammals, such as ___ and _____ reach much higher densities in edge habitats because they are able to take advantage of human resources (garbage), and return to the safety of the preserve.
Coyotes and Racoons
Taking this a step farther,raccoons in the US, and red foxes in England, have even penetrated urban areas to become part of the city, reaching high densities.
Raccoons and Red Foxes
Other mammal species cannot tolerate edge environments, ___ and ______ do not like humans and cannot live on the edge (in cases where they try, very bad things might happen.
Wolves and mountain lions
A species native to the United States.
It is a brood parasite, evicting the eggs of other species to replace them with its own.
They preferedge habitats. Now that forests are fragmented, there are few safe areas from them, and forest interior species such as bluebirds are suffering a major loss of fitness in some areas.
Cowbirds
Surviving areas of natural habitat often change because humans have fundamentally altered natural ecosystem processes.
Habitat Change and Disruption of Ecosystem
There are probably about 25, 000 species of orchids worldwide, and they are being lost faster than they can be classified.
Orchids are typically tightly coevolved in _______ relationships with other species, and the loss of any of these relationships can lead to extinction.
Mutualistic
A very diverse group of orchids that occupy a wide variety of habitats in the Northern Hemisphere. They are in decline even in protected areas, such as Indiana Dunes.
Lady’s Slipper Orchids
Human activities have altered their ecosystems.
Ladys’ slippers need a mutualistic fungus to germinate and grow for the first few years
Airborne nitrogen compounds (mostly from automobiles) effectively “fertilize” vast areas of ground and may put the mutualistic fungi at an ecological disadvantage.
Also, the widespread application of pesticides, the human tendency to groom and “clean up” areas of open sand and fallen wood, and the arrival of honeybees, have disrupted the ecology of pollination for orchids
Lady’s Slipper Orchids and Habitat Change/Disruption of Ecosystem
Salmon species have experienced dramatic declines over the past few decades due to a variety of factors, many of which result from human habitat modification.
Hydroelectric dams have resulted in increased juvenile mortality and made many habitats inaccessible to migrating salmon.
Pacific Salmon
Additionally, human logging and agriculture has silted and modified many of their upstream habitats, causing a drop in recruitment
Human activities are creating the worldwide faunal interchange.
This is an uncontrolled experiment in community ecology, with the potential result of a massive loss of gamma diversity worldwide caused by the loss of endemic species.
Introduction of Exotics
Most exotic species that arrive on new continents do not spread or establish themselves, but the ones that do often succeed spectacularly, causing change to native ecosystems that results in many extinctions.
Introduction of Exotics
discovered in Lake St. Claire near Detroit. It was introduced to the Great Lakes from the Caspian Sea, probably in the ballast water from a cargo ship, sometime around 1985
They have since spread throughout the Great Lakes region and throughout the Mississippi and Ohio River valleys.
Zebra Mussels
It forms dense clusters of individuals, and can clog the water intakes of electrical power stations, water stations, and other industrial facilities.
A very effective competitor. Extinction of native bivalves will almost certainly result from this introduction.
Zebra Mussels
incredibly effective filter feeders. They actually make the water much clearer, but alter native communities of organisms in the process. In the Hudson River, phytoplankton biomass decreased 85% after these invaded, zooplankton decreased 70% as a result.
Zebra Mussels
was introduced to Guam in the late 1940s, probably by hitching a ride in the wheel well of a plane.
Since that time, it has literally eaten most of the endemic birds of Guam to extinction.
Since there are no other native snakes in Guam (other than a blind, burrowing species), the bird fauna there evolved no natural defenses
Boiga Irregularis
competition and predation keep it in check, but the simpler ecosystem of Guam has allowed it to increase in numbers to up to 20 individuals per square acre of jungle (among the highest ever recorded for a snake).
It also causes other problems in Guam, including numerous power outages resulting from large numbers of snakes resting on power lines.
Boiga Irregularis
Cow-this huge sirenian mammal lived in the reached a length of 26 feet and could way seven thousand pounds or more. It existed on a diet of kelp, and could not dive or swim quickly.
It was delicious, and was hunted to extinction by sailors within 30 years of its discovery
Stellar’s Sea Cow
Overexploitation
What makes a species vulnerable to extinction? (5)
Endemism Rarity Small Population Size Ecological Specialization Beauty/Usefulness to Humans/Competitor with Humans
Species that are restricted to a particular, small area, are more vulnerable to extinction
Endemism
not the same thing as endeminsm, endemics can be very common in the restricted area where they do occur.
“Naturally rare” species have low population densities, but may be widely distributed and have respectable population sizes.
Rarity
We do not completely understand the ecological factors that make some species “naturally rare”, but when a common species gradually becomes rare, it is often a prelude to ____
“Naturally rare” species can be a challenge to conservation, because they are difficult to monitor and it is very difficult to ensure that sufficient habitat is set aside for them.
Extinction
Renders a species very vulnerable to extinction, through reduced genetic variation via genetic drift, the potential for inbreeding depression, and demographic stochasticity caused by random ecological disasters.
Small Population Size
more prone to extinction because there are only a few ways they can ‘fit themselves into” an ecosystem. They must have certain interspecific relationships in order to feed, obtain mates, have places to live, or maintain competitive superiority. The loss of other species in the community, or habitat change due to human activity, can change these factors, and render a formerly successful species vulnerable to extinction.
Ecological Specialists
ecological specialization
Humans-Humans have a way of killing all the pretty things, harvesting all the useful things, and hunting to extinction everything that could be perceived as a competitor.
Useful to Humans or a Competitor of Humans
fishermen in San Francisco Bay Area are prone to despising the ________, despite its important place in the ecosystem of the California Coast, because of its perceived status as a competitor. This is an example of
California Sea Otter
Useful to Humans or Competitor to humans
Crocodiles kill pets. Rattlesnakes, despite their critical role in ecosystems, are often despised in the Southwestern United States.
They are protected now, however, they were nearly hunted to extinction for their pelts. Species that cross the paths of humans sometimes suffer for it.
Useful to humans or a competitor to humans
Any conservation plan that does not take human economics into account is prone to failure. It is very difficult to set aside a habitat and protect it from all human activity.
The closest we have ever come are on military bases and nuclear test sites (the conservation effect was unintentional at first), and some private organizations (Nature Conservancy) buy natural land and simply fence it off.
Even these exceptional preserves have neighbors, and are occasionally eyed by developers and government reclassification.
The vast majority of preserves must balance the needs of human ecotourists, indigenous peoples, neighbors, and government budget considerations against conservation goals.
