CONSERVATON BIOLOGYLecture05 – Spring 2015 Althoff - reference Chapters 6-10

THREATS TO BIODIVERSITYPart II

Extinction Process

• Why are some species more vulnerable to extinction than others?SIMPLE ANSWER– ________________

• Examples from Hunter and Gibbs: a) bighorn sheep occupying semi-isolated ranges b) bird species on islands off the coast of Great Britain

Extinction ProcessBIGHORN SHEEP POPN ON SEMI-ISOLATED

MOUNTAIN RANGES

Persists

Extinction ProcessBIRD SPECIES (62 SPECIES) ON ISLAND OFF

THE COAST OF BRITIAN

Fail:

Why are some species rarer than others?

• Restriction to an _____________ type of habitat

• Limitation to a ________ geographic range

• Occurrence only at ______ population densities

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Restriction to an uncommon type of habitat

• May have resulted because they evolved ___________ characteristics that allow them to live there and nowhere else.

Ex. Naked mole rats; black-footed ferretsCave-dwelling invertebrates, fishes,

and amphibians• Some may been successful there simply

because they ________ successful any place else (i.e., cannot out compete other species).Ex. Steamboat buckwheat

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Limitation to a small geographic range

• May have resulted from geographic _______Ex. Populations on Islands, in a lake

(cichlid fishes in Lake Malawi Africa)• ______ range of “tolerable” conditions can

result in small geographic rangeEx. Many Amazonian plant species

evolved in special soil conditions.Ex. Plant species in bogs where very

acidic conditions

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Occurrence only at low population densities

• Body size: large animals take lots of spaceEx. Elephants, moose, elk (in certain

settings)• Small density populations persist because they do

well when they __________ with one another.Ex. Wolverines, Hawaiian hawk

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Usually, a species exhibits just ____ of the 3 basic “rare” charactistics, but…

• A few species may have 2 or even 3 of the “rare” characterisitics

• Rare habitat

• Small geographicrange

• Low popn density

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Why are Rare Species Usually MoreVulnerable to Extinction than Common Species?

• #1 likely reason: rare species have a greater chance of being pushed into extinction because of _____________________—especially if they have a small geographic range….about ¾ of all known extinctions since 1600 have been island species

• Other reasons could include: _______________ ______ (especially if biased against females), ______________ problems (genetic drift, inbreeding, and bottlenecks)

Why are Some Species Particularly Sensitive to Human-induced (anthropogenic) Threats?

• __________________________________ : low reproductive rate (small number of progeny, long generation time, etc.), limited dispersal capabilities, inflexible habitat requirements, etc.

• ______________: singled out by people. Examples include wolves and African wild dogs (to eliminate threat of livestock loss), passenger pigeons (edible), diamond-backed turtles (edible)

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Why are Some Species Particularly Sensitive to Human-induced (anthropogenic) Threats? …

con’t

• ____________________: those tied to ecosystems preferred by humans are more at risk—think areas with fertile soils (prairies vs. agriculture) or abundant water resources (for hydroelectric power, etc.)

• ________________________: Fragmentation can reduce extensive tracts of one habitat-type or another (think many large terrestrial carnivores/ predators).

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Patchy Distributions and Metapopulations

• ______________ = model of population structures whereby each patch of habitat contains a different subpopulation of a species. A group of “patch” populations is collectively a metapopulation.

Metapopulation __ Metapopulation __

Examples of Metapopulations• Prairie chickens• Sage grouse• Black-footed ferrets• Piping plovers• Green salamanders

Keep in mind….

• ______ species that are distributed in habitat patches are composed of metapopulations. Often bird species—being highly mobile—are not as likely to exhibit metapopulation structure

• Metapopulations is a concept associated with _________________________ ____________________

• Metapopulation dynamics can be viewed as two types of subpopulations & two types of processes……

Subpopulations & Processes Associated with Metapopulation Dynamics

• Two subpopulation types: 1) ________ popn

2) ________ popn

• Two processes:1) local ______________

2) ______________ (recolonization)

Source vs. Sink (sub)populations

• Source: produce substantial number of _________ that ___________________

• Sink: do ____ produce enough individuals to maintain their local numbers and typically only continue to exist through _______ __________ from other subpopulations (aka source subpopulations.

Sink (sub) populations….

• Are inherently _____ to go ______ (aka local extinctions) because the habitat they occupy is either too small or of too poor quality to regularly (for years and years and years) produce enough offspring to remain sustainable

• And, often can be colonized (or recolonized) by dispersing individuals from source populations because they appear to be suitable habitat for breeding/reproducing

• Cache River prothonotary warbler subpopulation (Wing & Prayer video)

• Dickcissel population in Central Prairie

Sink (sub) populations….examples

Sutton CenterOklahoma

Cowbird brood parasitism of Dickcissels

In summary…• The metapopulation concept offers a framework for

understanding the dynamics of populations in _________ landscapes (i.e., think fragmentation)

• Subpopulations are subject to (local) extinction and colonizations (recolonizations)….as influenced by ____________ subpopulations within the metapopulation

• Patchy landscapes (aka fragmentation) is becoming more and more common because of _________ activity.

• However, do not assume ALL at-risk species conform to the metapopulation concept

In summary…con’t• Some species are rare than others because they are

1) restricted to an uncommon habitat type, 2) are limited in their geographic range, and/or 3) occur only a low population densities.

• In rare instances, a species might have all 3 of the above characteristics.

• Many species are at-risk due to anthropogenic influences:1) limited adaptability & resilence2) human attention3) ecological overlap4) large home-range requirements