Lecturer: James Reeler

Material by: Sam Hopkins

Habitat loss is when a habitat is changed from one type to another

Habitat fragmentation is where habitats are divided into smaller parts

WHAT IS HABITAT LOSS AND WHAT IS HABITAT LOSS AND FRAGMENTATION ?FRAGMENTATION ?

Habitat loss reduces the amount of habitat available

Thought to be the most important threat to biodiversity at the moment

Fragmentation results in the pieces of habitat increasing in insularity with larger edges as well as a loss of total habitat

WHY IS IT SO IMPORTANT ?WHY IS IT SO IMPORTANT ?

Habitat loss and fragmentation are caused primarily by humans

For example

Building

Draining wetlands

Nutrient enrichment

Grazing

Cultivation

Dredging

Stopping fire

Clearing

WHAT CAUSES HABITAT LOSS AND FRAGMENTATIONWHAT CAUSES HABITAT LOSS AND FRAGMENTATION

As the habitat becomes fragmented the edge of the forest increases

The edges are different to the interior of the fragment in climate, soil environment and species composition

Each fragment of habitat is surrounded by a “matrix” which is the term used for the modified habitat

EDGE EFFECTS EDGE EFFECTS 11

The species at the edge of the habitat tend to differ from the ones in the centre of the fragment

This is seen in the vegetation present in forest fragments where

Stem density increases at the edge

Species richness increases

Shade intolerant species grow at the edge

Shade tolerant species stay in the centre

Tree mortality at patch edge

EDGE EFFECTS EDGE EFFECTS 11

On Madagascar 90% of the forests have been lost

The remaining forests persist as small isolated fragments

This increases the numbers of edges

It is suggested that these edges will affect the herpatofauna as they have quite specific physiological needs

EDGE EFFECTS –EDGE EFFECTS –HERPATOFAUNA OF MADAGASCAR HERPATOFAUNA OF MADAGASCAR 22

In one study the edge effects were found to influence the distribution of many species

The study was conducted in patches of rainforest with anthropogenic scrub in between

Some species only inhabited the interior of the forest

Some species preferred the edge of the forest

It was found that the season affected certain species affinity for the edge or interior

EDGE EFFECTS –EDGE EFFECTS –HERPATOFAUNA OF MADAGASCARHERPATOFAUNA OF MADAGASCAR 22

Edge avoiders

Mantidactylus boulengeri

Interior avoiding

Mabuya elegans

Seasonal

Mantidactylus bicalcaratus

Omnipresent

Hemidactylus mercatorius

Edge avoiding reptiles and amphibians are more prone to extinction

EDGE EFFECTS –EDGE EFFECTS –HERPATOFAUNA OF MADAGASCAR HERPATOFAUNA OF MADAGASCAR 22

As each fragment of habitat is surrounded by an altered habitat it is possible to look at these fragments as islands

A lot of the theory on island communities is relevant to habitat fragments

The risk of local extinction in single fragments becomes higher as the fragment is often too small to support a viable population

Re-colonisation from other fragments is possible however this depends upon the distance of the nearest fragment

ISLAND BIOGEOGRAPHYISLAND BIOGEOGRAPHY 3 3

A number of studies have looked at the island effect on mammals, birds and lizards in Western Australia

There are 23 preserves varying in size from 34 – 5119 hectares

The birds did not seem to be affected by this fragmentation, possibly due to their ability to re-colonise areas using shrubby growth and tree lined roads

The lizards and mammals were affected by the isolation as if their were on an oceanic island

Some of the lizards and bird had already become extinct in some of the preserves

ISLAND BIOGEOGRAPHY ISLAND BIOGEOGRAPHY 33

70% of wetlands in southern Ontario have been destroyed

Much of this land is now used for agriculture

In a study on the anurans in the area, anuran diversity as well as density decreased in agricultural areas as well as land down stream from the agriculture

This was seen for 7 species of frog

HABITAT DESTRUCTION CAUSES SPECIES TO DECLINE –HABITAT DESTRUCTION CAUSES SPECIES TO DECLINE –ANURAN SPECIES IN ONTARIO CANADAANURAN SPECIES IN ONTARIO CANADA 55

The micro frog (Microbatrachella capensis) is now on the IUCN red data

list as critically endangered 6

This has been caused by habitat destruction

The habitat that the frog relies on is sand plain fynbos, it is unique in its composition of acidophilic plants such as ericas and proteas 7

FRAGMENTATION CAUSES SPECIES TO DECLINE –FRAGMENTATION CAUSES SPECIES TO DECLINE –

THE MICRO FROGTHE MICRO FROG

Over half of the sand plains fynbos on which the micro frog

relies is under human settlement and only 0.013% of the fynbos

type remains 7

One of the few remaining sites is in centre of Kenilworth race course

It has only lasted here because of the protection that the racecourse has provided

As you can see from the photo it is surrounded by human settlement

The area is only 56 hectares

FRAGMENTATION CAUSES SPECIES TO DECLINE –FRAGMENTATION CAUSES SPECIES TO DECLINE – THE MICRO FROGTHE MICRO FROG

Where habitat is destroyed or fragmented some animals benefit

Grey squirrels

Rats

Foxes

Canadian Geese

Pigeons

European sparrows

House mice

These species are often thought of as pests

SOME SPECIES BENEFIT SOME SPECIES BENEFIT

A controversial concept is to have corridors between fragments to allow

the movement of species

The idea behind a corridor is that a strip of natural habitat is allowed to remain in

the unnatural matrix

It should link two fragments of habitat that are being conserved

This is meant to allow for local extinctions and re-colonisation

In practice it is not so simple

SO WHAT CAN WE DO ?SO WHAT CAN WE DO ?

There are arguments and studies supporting and refuting the use of corridors

For a look at a conservation corridor plan in Minnesota go to www.de-chant.com/tim/nhc/index

CONSERVATION CORRIDORS CONSERVATION CORRIDORS

Fahrig and Merriam (1985) 8 tested a model that compared the age structure and population size of patches of habitat that were linked or not

They then applied the model to the white footed mouse (Peromyscus leucopus)

The white footed mouse lives in patchy forests and doesn’t like open areas

They applied the model to populations of mice that were isolated or linked to another population by a corridor

They found that isolated populations had a lower growth rate

FOR CONSERVATION CORRIDORS FOR CONSERVATION CORRIDORS

A study by Aars and Ims (1999) 9 focused on voles

They looked at population sizes and the genetics of the population

The voles had the same population size with or without the corridor

The corridor enhanced the movement of female voles from one population to the other

The corridor did not affect the movement of males from one population to the other

This small increase in movement by the female voles could enhance genetic diversity within the fragmented populations

FOR CONSERVATION CORRIDORS FOR CONSERVATION CORRIDORS

An overview by Mann and Plummer (1993) 10 discussed the use of habitat corridors

The report was written after a conference where only 5 out of the 36 papers presented empirical data and three of them showed that animals rarely move along them

The problems with corridors are:

Fire

Disease

Introduced species

Costs

AGAINST CONSERVATION AGAINST CONSERVATION CORRIDORS CORRIDORS

The largest example of an across border (transfrontier) park is in Southern Africa

It is an agreement with Kruger in South Africa, Limpopo in Mozambique

ACROSS BORDER PARKS ACROSS BORDER PARKS 1111

and Gonarezhou in Zimbabwe

The area includes 4 main habitat types and boasts species numbers of at least 147 mammals, 116 reptiles, 49 fish, 34 frogs, 500 birds and 2000 plants

It is about 40,000 square km

Aims to allow more natural migration patterns by taking down fences

1. Freidenburg, L. (1997) Physical effects of habitat fragmentation in Fielder, P. and Kareiva, P. Conservation Biology for the coming decade pp 66-79

2. Lehtinen, R. M. et al. (2003). Edge effects and extinction proneness in a herpatofauna from Madagascar. Biodiversity and conservation 12: 1357-1370

3. Cox, G. W. (1997) Conservation biology. Pp 123- 131

4. Debinski and Holt (2000) A survey and overview of habitat fragmentation experiments. Conservation Biology 14: 342-355

5. Bishop, C. et al. (1999) Anuran development, density and diversity in relation to agricultural activity in the Holland river watershed, Ontario, Canada (1990- 1992). Environmental monitoring and assessment 57: 21-43

6. De Villiers, A. L. (2004). Microbatrachella capensis (Boulenger, 1910). In Atlas and red data book of the frogs of South Africa, Lesotho and Swaziland. Eds Minter, L.R., Burger, M., Harrison, J. A., Braack, H. H., Bishop, P. J. and Kloepfer, D. pp 241-244

7. McDowell, C. (1989). Conservation and horse racing: the unseen connection. Veld and Flora 75: 36-39

8. Fahrig and Merriam (1985) Habitat patch connectivity and population survival. Ecology 66: 1762- 1768

9. Aars and Ims (1999) The effect of habitat corridors on rates of transfer and interbreeding between vole demes. Ecology 80: 1648- 1655

10. Mann and Plummer (1993) The high cost of biodiversity. Science 260: 1868- 1871

11. www.environment.gov.za/projprog/tfcas/gltp

REFERENCES REFERENCES