Habitat loss

Habitat loss refers to the decline of habitats through displacement, destruction, degradation and other forms of landscape change. Direct habitat destruction is the main cause of global biodiversity loss . These factors cause the decline in animal and plant populations directly and to a much greater extent than changes due to climate change , habitat fragmentation and invasive species .

"Man does not primarily cause the decline in the diversity of organisms directly through exploitation or malicious action, but through the destruction of natural habitats, which inevitably follows from the growth of human population and their activities."

- DW Ehrenfeld (1988)

Examples

Global situation

Many habitat losses are due to human activity. The disappearance of habitats caused by civilization is based on secondary effects of population growth and economic expansion . A disorderly selection of the main factors includes deforestation / deforestation, especially tropical rainforests , pollution and land sealing . In contrast to natural evolution, habitat destruction usually leads to a comparatively sudden reduction or destruction of species . Besides the problem of invasive species, habitat destruction is the most important reason for the global reduction in biodiversity .

The following diagram gives an overview of the worldwide loss of habitats and the proportion of threatened species in the respective habitats:

	Worldwide habitat loss and proportion of threatened species
	Habitat loss (%) Share of threatened species (%)
Tropical forests	30th 22nd
Temperate forests	48 15th
Northern coniferous forest belt	2 5
Grassland and scrubland ¹	57 17th
Deserts and tundras	21st 12
Seagrass meadows	29 16
Mangroves	37 11
Coral reefs	20th 27

¹including Mediterranean habitats

Examples of effects on groups of animals

The loss of a habitat structure that has diverse niches affects terrestrial and hydric and marine organisms.

One example are the critically endangered river dolphins . They are no longer hunted today, but are threatened with extinction or have already become extinct due to the destruction of the natural river courses and the change in their river habitat. The Chinese river dolphin ( Lipotes vexillifer ) population has declined due to water pollution , accidental killing in fishing nets, and the construction of dams and other regulatory measures. The Chinese river dolphin may have already become extinct, the Amazon dolphin ( Inia geoffrensis ) is endangered according to the IUCN and there is no precise information about the La Plata dolphin ( Pontoporia blainvillei ), but this species is probably also threatened.

Reinforcing factors

The driving and reinforcing factors of global habitat loss have been the subject of many scientific studies. In 2002 Geist and Lambin examined which factors actually underlie the loss of tropical rainforests . Their study presented the various factors in relation to one another and is based on 152 case studies in which one of the values ​​collected played a significant role. According to this, the reasons for habitat loss are mostly economic (81 percent), followed by political reasons (institutional or policy factors, 78 percent), technological reasons (70 percent), cultural and sociopolitical factors (66 percent) and demographic reasons (61 percent) . The driving economic reasons include the accelerated growth of the timber industry and the marketing of timber.

Stochastic proof

The loss of habitat is scientifically described within the framework of the theory of metapopulation . Under the usual assumptions for a metapopulation approach, a habitat loss is written as follows: Let the proportion of habitats occupied at the time and e and c the probability of extinction or probability of colonization per time step. Then the loss of habitat results in : ${\displaystyle p}$ ${\displaystyle t}$ ${\displaystyle L}$

${\displaystyle {\frac {dp}{dt}}=cp(1-(p+L))-ep}$

In words, the model equation says: The change in the proportion of occupied habitats over time is obtained by adding the habitats newly occupied per unit of time and subtracting the habitats lost in the same time step . The number of newly colonized habitats depends on the proportion of habitats already occupied . ${\displaystyle cp(1-(p+L))}$ ${\displaystyle ep}$ ${\displaystyle 1-p-L}$

This leads to a lowered base reproduction rate

${\displaystyle R_{L}={\frac {c(1-L)}{e}}}$

The threshold value for persistence is, as intuitively clear, at and thus at ${\displaystyle R_{L}=1}$

${\displaystyle R=(1-L)^{-1}}$.

This clearly means nothing other than that in every time step the same number of habitats are occupied as they are lost. Thus, the critical habitat loss leading to extinction results as:

${\displaystyle L_{c}=1-{\frac {1}{R}}}$

Initiatives and politics

Since the loss of original habitats is mostly caused by direct or indirect human influences, it is also a topic of politics and politics. At the European level, nature conservation organizations want to create a pan-European ecological network and have founded the EECONET Action Fund for this purpose .

view

Global population growth will rapidly impact land use and overexploitation . Soil sealing is increasing in populous countries like Germany. Large-scale modern agriculture is cited as the main factor in land use changes and thus also in the loss of cultivated landscapes . In less developed countries, clearing or overexploitation of land leads to the loss of largely unused (“wild”) ecosystems and thus often to the disappearance of animal and plant species. In Germany, the federal government's biodiversity action program aims to slow down the process. Globally, the actors want to slow down habitat losses with political agreements such as the Convention on Biological Diversity .

literature

• JD Murray: Mathematical Biology. An introduction. Interdisciplinary Applied Mathematics Volume 17. 3rd ed. 2001. Springer. ISBN 0-387-95223-3

Interesting publications:

• Nicole Sonntag ( FTZ west coast ): Investigations into habitat loss and behavioral changes of sea birds through the offshore project alpa ventus ( PDF )
• Darren J. Bender, Thomas A. Contreras, Lenore Fahrig (1998): Habitat loss and population decline. Ecology 79: 517-533. doi : 10.1890 / 0012-9658 (1998) 079 [0517: HLAPDA] 2.0.CO; 2 . A meta-analysis of 25 studies on the topic. ( PDF )

Individual evidence

1. ^ DW Ehrenfeld: Why put a value on Biodiversity? in: Edward O. Wilson, Frances M. Peter (editors): Biodiversity. National Academy of Sciences (US), Smithsonian Institution, 1988, Chapter 24. Quoted from Richard B. Primack: Conservation Biology '. Spectrum Academic Publishing House, 1995
2. ^ WR Turner, M. Oppenheimer, DS Wilcove: A force to fight global warming . In: Nature . 462, No. 7271, 2009, pp. 278-279. PMID 19924191 .
3. ↑ Helmut J. Geist , Eric F. Lambin (2002): Proximate causes and underlying driving forces of tropical deforestation. BioScience 52 (2): 143-150 doi : 10.1641 / 0006-3568 (2002) 052 [0143: PCAUDF] 2.0.CO; 2