Habitat fragmentation #I14 September 2009 – Pringle lecture

l. Components of fragmentation A. Reduction in total amount of habitat type B. Apportionment of remaining habitat into smaller and more isolated patches

II. What constitutes a barrier?

III. Biological responses to habitat fragmentation A. initial exclusion B. isolation C. island-area effects D. edge effects IV. The case of migratory songbirds

V. Protecting wildlife/biotic integrity in a fragmented landscape: Challenges facing remnant natural areas

I. Components of Habitat Fragmentation

A. Natural heterogeneity vs fragmentation caused by humans (rich internal patch structure vs simplified patches)

B. Biota in human-altered fragmented landscapes are affected at different levels of biological organization

a. changes in gene frequencies of local populations

b. continent wide changes in species distribution and ecosystems (Panda Example)

Slide 6

Habitat loss and fragmentation Increasingly leadingto ex situ breeding andconservation efforts

Components of habitat fragmentation: apportionment of remaining habitat into smaller and more isolated fragments

II. What constitutes a barrier?

• Species Specific

• Cumulative effects -dams in rivers -roads in parks -canals -power lines -fences -fire lands -other ???

Dams as barriers

Roads as barriers

Road Impacts:

• Animal vehicle collisions cause 200 deaths per year in the US and cost US 1 billion annually in property damage

• 35 million reptiles and frogs per year in Australia• 43,002 deer in Pennsylvania in 1990• 30,306 deer in Ohio in 2002• >10,000 deer per year in Kansas• 102 black bears in North Caroina in 2002

• Ecological hot spots of mortality:

Roads as avenues for invasion by humans and exotic species

Initial road 20 yrs later

The case of hedgerows in Britain and the importance of protecting historical landscape features

in highly fragmented landscapes

What constitutes a barrier for domestic livestock is a corridor for ‘wildlife:

The ‘wildlife’ in hedgerows:

Many small mammals house mice, door mice, shrews, weasels, voles

Most of Britain’s woodland birds use hedgerows at least some of the time

High diversity of plants relative to surrounding countryside

Greater number of species in older hedges

In Britain, roughly a quarter of the hedgerows (96,000 miles) were removed between 1945-85. An additional 56,000 miles lostbetween 1984-90

III. Biological responses to habitat fragmentation

A. initial exclusion

B. isolation

C. island-area effects

D. edge effects

Initial exclusion, isolation and consequent loss of biota

Reindeer in southern Norway

Island Area Effects: Competition and overgrazing

Edge Effects

• temperature,

light, humidity,

wind, fire

• predation

• exotic species

• disease

• pollution

Edge Effects: increased vulnerability to predation

Nest predators in fragmentedLandscapes

•Cowbirds parasitize the nests of >200 bird species

•Originally restricted to the northern part of the Great Plains

Endangered Kirtland’s warbler - highly parasitized by cowbirds

Brown headed cowbird chick in nest of yellow warbler

Smaller-bodied host birds have less chance of raising any of their own young than do larger-bodied birds

Solutions?

Humanely disposing of cowbirds

Edge effects: Greater vulnerability to invasion by exotics

Edge Effects: Enhanced incidence of infectious disease

Are migratory song bird declines in North America primarily a result of habitat fragmentation in temperate regions or habitat destruction in the

tropics?

Where have all the birds gone?

Decline of migratory songbirds:

• Reproductive failure in temperate breeding areas due to habitat fragmentation

• Destruction of tropical habitat

Protecting migratory songbirds:

• Recognizing the importance of intact source areas- i.e. large areas of intact forest which serve as refuges producing surplus birds that can later disperse and re- populate sink areas

• Restoring forests in areas that are currently sinks

Habitat fragmentation #I

I. Components of fragmentation A. Reduction in total amount of habitat type B. Apportionment of remaining habitat into smaller and more isolated patches

II. What constitutes a barrier?

III. Biological responses to habitat fragmentation A. initial exclusion B. isolation C. island-area effects D. edge effects IV. The case of migratory songbirds

V. Protecting wildlife/biotic integrity in a fragmented landscape: Challenges facing remnant natural areas