Lecturer: James Reeler Material by: Sam Hopkins
Dec 22, 2015
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