What Makes Populations and Species Vulnerable?

What Makes Populations and Species Vulnerable?

Brook Milligan

Department of BiologyNew Mexico State University

Las Cruces, New Mexico [email protected]

Fall 2009

Brook Milligan What Makes Populations and Species Vulnerable?

mailto:[email protected]

Rarity

What makes populations and species vulnerable?

RarityBut . . .Many types of rarity exist

Examples of rarity

Argyroxiphium macrocephalum (Haleakala silversword):limited to Haleakala Volcano, Maui, Hawaii, but very commonwithin craterSetaria geniculata (knotroot bristlegrass): distributed fromMassachusetts to California, south to Argentina and Chile; notselective regarding habitat, but everywhere sparse; 2 specimensin NM (Hidalgo and Dona Ana Counties)


Rarity

What makes populations and species vulnerable? RarityBut . . .

Many types of rarity exist

Examples of rarity



Rarity

What makes populations and species vulnerable? RarityBut . . .Many types of rarity exist

Examples of rarity



Dimensions of Rarity

Geographic distribution

narrowwide

Habitat requirements

restrictedbroad

Local population size

everywhere smallsomewhere large


British flora survey

160 species categorized by experts

Geographic DistributionWide Narrow

Habitat Specificity Habitat SpecificityLocal Population Size Broad Restricted Broad Restricted

Somewhere large 58 (36%) 71 (44%) 6 (4%) 14 (9%)common

Everywhere small 2 (1%) 6 (4%) 0 (0%) 3 (2%)


Factors inreasing vulnernability

Rarity

narrow geographic rangeone or a few populationssmall population sizespecialized niche requirementsrestriction to rare habitatlow population density

Correlates of rarity

Direct human exploitation

Correlated effects of human-induced habitat alteration

Evolutionary indications

Complex habitat requirements

Immediate indicators



Rarity


large home rangelarge body sizeineffective dispersers








Rarity



subject to human hunting or harvesting







Rarity




aggregate permanently or temporarilycharacteristic of stable, pristine environmentsno prior contact with humans






Rarity





low genetic variabilityrelated to extinct or threatened species





Rarity






seasonal migrants




Rarity







declining population size


International Union for the Conservation of Nature (IUCN)system

Categories of species

Categories applicable to worldwide status

extinctextinct in the wildcritically endangeredendangeredvulnerablenear threatenedleast concern: include widespread and abundant speciesdata deficientnot evaluated

Additional categories applicable to regional status

regionally extinctnot applicable: species not occuring naturally in a region or arare migrant


Distribution of Species

Total IUCN Red List: 41,415 species

Extinct: 785 species

Extinct in the wild: 65 species

Endangered and vulnerable: 16,306 species

critically endangeredendangeredvulnerable


Status of Major Taxonomic Groups

Endangered and vulnerable species

Mammals: 25%

Birds: 12.5%

Amphibians: 33%

Assessed plants: 70%


IUCN Evaluation criteria

Population size: total number of mature individuals

Geographic range: total geographic area (B) currently alive(D)

Population dynamics

observable decline in numbers of individuals (A)predicted decline in numbers of individuals (C)extinction probability: probability of extinction within aspecified time or number of generations (E)

rarely used, but correlated with other factorshow to calculate: PVA methods upcoming


IUCN Red List Criteria v3.1

IUCN Red List Criteria v3.1A. Populationsize B. Geographic C. Declining D. Pop. E. Extinction

Category reduction1 range pop. size size probability

% km2 indiv. indiv. % Years Gen.Critically endangered ≥80–90 <10-100 <250 <50 ≥50 10 3Endangered ≥50–70 <500–5,000 <2,500 <250 ≥20 20 5Vulnerable ≥30–50 <2,000–20,000 <10,000 <1000 ≥10 100Source: http://data.iucn.org/themes/ssc/redlists/RLcats2001booklet.html1. Reduction over 10 years or 3 generations.


Case study: Rocky Mountain locust (Melanophus spretus)

Major agricultural pest in 1870s

$200 million in crop damage between 1873 and 1877 inColorado, Nebraska and other states“Greatest concentration of animals” (The Guinness Book ofWorld Records)

A swarm of Rocky Mountain locusts that flew overNebraska on July 20–30, 1874, covered an areaestimated at 198,000 square miles (almost twice thesize of Colorado). The swarm must have containedat least 12.5 trillion insects with a total weight of27.5 million tons.



Major agricultural pest in 1870s

$200 million in crop damage between 1873 and 1877 inColorado, Nebraska and other states

“Greatest concentration of animals” (The Guinness Book ofWorld Records)

A swarm of Rocky Mountain locusts that flew overNebraska on July 20–30, 1874, covered an areaestimated at 198,000 square miles (almost twice thesize of Colorado). The swarm must have containedat least 12.5 trillion insects with a total weight of27.5 million tons.


Rocky Mountain Locust Distribution



Current status

Now (virtually?) extinct

Historical causes

Permanent and migratory phases of life cycle

Waves of expansion from Rockies to plains

Vulnerable because of habitat limitation in permanentbreeding grounds: riparian regions in Rocky Mountains ofColorado

Conservation status

Rare or not?

Conserve or not?


What Makes Populations and Species Vulnerable?

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