An accepted goal of conservation is to build a conservation network that is resilient to fragmentation and environmental change. However, fragmentation is a relative concept as well as connectivity. Effective corridors should provide suitable and reliable connectivity among habitats across scales for species mobile or less mobile for gene exchange under uncertainty and change. However, often a "static" vision of landscapes is adopted (i.e. the cartography of land uses/covers) whereas landscapes (habitats included) are dynamic. Indeed, they do change either under different seasonal conditions, or under multiple driving forces like, for instance, climate change. As a result, what we are looking for, i.e. fragmentation or effective corridors, can systematically change on the map, and what is fragmented or suitable as corridor under certain conditions could not be suitable or fragmented when season, conditions or the set of focal species are changed. Just because we are not so good in predicting the future and what could be a suitable network sustaining biological diversity and gene exchange, we have to rely on past time series (at a suitable scale) to define the trajectory of every landscape piece to see whether it is predictable or not, that is, if it is persistent or not. Once you get a "predictability" map then you can think of applying different modelling tools to derive, under uncertainty; what possibly could be an effective corridor network and a suitable fragmentation for the future. So you could discover that along with "classical" green and blue ways other elements in the landscape could be crucial for the network based on their predictability. You could also discover which unpredictable landscape pieces are crucial for the maintenance of the overall connectivity in the face of climate change and try to transform them in "persistent" through planning and management efforts. See, for instance, the paper "Highlighting order and disorder in social–ecological landscapes to foster adaptive capacity and sustainability" recently appeared in Landscape Ecology.

The same principle should be applied to fragmentation/connectivity for marine systems (see Modeling population connectivity by ocean currents, a graph-theoretic approach for marine conservation appeared in Landscape Ecology). Indeed, for many marine species, population connectivity is determined largely by ocean currents transporting larvae and juveniles between distant patches of suitable habitat. So, connectivity relies on the persistence of ocean currents suggesting areas that might be prioritized for marine conservation efforts and that are working like "stepping stones" in the maintenance of the overall network. On the other hand, you might identify "new" candidate stepping stone areas in case of predicted changes in the oceanic current pattern due to climate change. Unfortunately most of marine biologists and ecologists involved in marine conservation do not consider the importance of ocean currents.

Dear Robert,

There is a large body of literature on the effects of fragmentation on biodiversity from a field project on habitat fragment sizes at Manaus in the Brazilian Amazon during the 80s-90s up to date. This review is also very good: L Fahrig. 2003. Effects of habitat fragmentation on biodiversity. Annual Review of Ecology, Evolution, and Systematics. JSTOR.

Cheers!

You can find some information about the Biological Dynamics of Forest Fragments Project (BDFFP) in this site of the Smithsonian Tropical Research Institute:http://www.stri.si.edu/english/research/facilities/affiliated_stations/bdffp/index.php

Thanks a lot for the references! Manuel, the review is interesting, since it distinguishes between fragmentation and habitat loss and also adresses that there might be positive effects of fragmentation. However, the idea of allopatric speciation processes fostered by fragmentation (barriers for gene flow) is not discussed. Are such processes unlikely because they require much time and anthropogenically induced changes in landscapes are too dynamic? Anyway, I agree with Fahrig who says "...led researchers to ignore the possibility that fragmentation per se could have a positive effect on biodiversity."

Hi robert talk to karthikeyan vasudevan.. Has done tremendous work on fragmentation...send him a message..he will surely respond or message me i will give his mail id...

Whether habitat fragmentation leads to a decrease or increase in diversity is probably very much scale-dependent. Do we talk about 10 days of a human-induced fragmentation process or do we consider natural processes which took millions of years? Are the remaining fragments only a few hectars large or do they reach thousands or millions of square kilometers?

Global palaeodiversity studies often link the Mesozoic diversity increase of marine invertebrates to the contemporaneous break-up of the supercontinent Pangaea into smaller continents (and thus the fragmentation of shelf areas), see e.g.

http://www.nhm.ac.uk/resources-rx/files/palaeontology07-18131.pdf

In my opinion habitat fragmentation affects biodiversity in different ways! First, I agree with Michael reply, so what do you mean with fragmentation? Which is the scale? This is a good reference for explain it

McGarigal, Cushman, Regan. 2005. Quantifying Terrestrial Habitat Loss and Fragmentation: A Protocol.

Moreover, testing the effects of fragmentation on biodiversity, should be strongly related with the context of the analysis... Specialist species can be negatively affected as well as generalists can be positive affected!

Fragmentation may paradoxically increase diversity by creating new species, when there is a barrier to breeding between groups. I have seen that here in Northern California with native grass populations that when are isolated, create genetically fixed ecotypes, like you can see in my common garden study at http://www.ecoseeds.com/common.html.

I agree that the accuracy of a question is essential for having a productive exchange of informations. My question does not appear accurate, however, I have received very helpful information regarding this subject, thanks a lot to everybody. Michael, do you think populations achieve reproductive isolation after 10 days of a human-induced fragmentation process? Craig you got my point. Are these grasses reproductively isolated? Are there more studies or examples?

Fragmentation in most cases decreases biodiversity. if few species remain and multiply, it does not increase biodiversity. As apart from barriers to gene flow, inter-species pollination also decrease. In such a case an invasive species appears, remaining biodiversity also finish. Wildlife is highly affected by fragmentation an in this respect suggestion by gul e Arzoo is highly significant.

@ Michael Buchwitz, nice answer. I also agree with M. B.

In my perception, if fragment size sub-population remain constant over small area for minimum time scale, it will not favor speciation process. But if fragmented area retains species for larger time scale then it may support your opinion.

Though in general sense, habitat fragmentation reduce biodiversity. I think species competitive ability may be an important aspect if functionally similar species are dominant in the fragmented area. Functionally similar species compete more for resource and hence reduce diversity. It depends on resource requirement, stress tolerance and niche-partitioning of species. If the functionally similar species able to cope with this situation then these will persist, otherwise not.

Any time populations of a plant or animal species is isolated to interbreeding, that can create new ecotypes and ultimately over time, new species. That fragmentation can be accelerated by impacts from the environment like Global warming, and looking at the ecotype question and what factors create ecotypes, may help to see what happens when populations get fragmented and isolated. I have a list of ecotype references from 1880-1996 for plants at http://www.ecoseeds.com/juicy.gossip.three.html

Sonia, my opinion is that we have to differentiate and fragmentation does not per se in- or decrease biodiversity.

Ludovcio, thanks a lot for the reference to the review, definitely a vote! I think I found a satisfactory answer to my question.

"The empirical evidence collected to date suggests that the effects of fragmentation per se on biodiversity are generally weaker than the effects of habitat loss. In addition, the effects of fragmentation are as likely to be positive as negative, and depend fundamentally on the interaction between habitat patterns and the ecological requirements and capabilities of the organism." (Regan 2005)

However, further reading recommended

http://www.umass.edu/landeco/teaching/landscape_ecology/labs/fragprotocol.pdf

Studies has shown that most important than the size of the fragment is the shape that it has for some communities. Also the level of fragmentation and the "permeability" of the environment around can influence a lot the possibility of genetic flow.

I can't remember if it's a portion of the discussion I needed to cut on my dissertation final file. But I can try to find the references I used.

There are some interesting books that you can download online published by my government about this subject. Unfortunately not all them available in English.

Let me know if I can help more in this discussion.

Of course, every information is welcome!

Most researchers look at habitat fragmentation as s a process involving both habitat loss (composition) and the breaking apart of habitat (configuration). Most of fragmentation researches do not differentiate between these two effects, and that has led to several problems in the interpretation of the effects of fragmentation on biodiversity. In this respect I would suggest to read the review by Lenore Fahrig, The effects of fragmentation on biodiversity, in Annual Review of Ecology, Evolution, and Systematics, Vol. 34 (2003).

I want to comment on the most recent contributions.

My study of the 109 fragments of native grass populations in the SF Bay area in 1991, the common garden study and ecotype web article at http://www.ecoseeds.com/juicy.gossip.three.html, studied contiguous species of grasses like Bromus carinatus, that originally covering the nine counties that we surveyed.

Where we found the most genetic diversity was at the environmental edges for the species--the extreme low rainfall edge, the extreme soil type edges, and the extreme climate variations within the smallest space, which was SF itself, and these extremes created ecotypes that had probably existed for eons,

However, by fragmenting a population, you are both creating barriers for future gene exchanges, and also creating a whole lot more edges. So as long as the new fragmented populations can reproduce and survive on their new island homes, then their isolation over time will create new species, and the new edge effects created by the fragmentation is a new environmental factor to help push in that direction. I have an image from my web article, of three new species currently evolving from B. carinatus at the edges, at http://www.ecoseeds.com/bromusmess.jpg.

If we look closely at fragmented native grass populations, we might be able to see evolution in action, and we might be able to see the edge effect impacts of the fragmentation on those changes. Since most of our North American native grass populations are already fragmented, there is an excellent opportunity to do studies in any of the lower 48 USA states, to answer this question that has been posed by Robert from Bolivia., with measurements and data,

Another area of study that could help answer this question, is genetic changes of isolated old plantings of exotic grasses, and see if they evolve over a short period of time. In California, we have introduced and naturalized over 1,000 exotics, many that have become widespread across the State over the last 100 years. I am in the process of collecting seed samples to tackle that question in the future--are these widespread exotics evolving where they were introduced only a few decades ago?

Hi,

My MSc thesies in a bout road building in natural park and the fragmentation that happen between 2 part of road. in my project at first time we face to decrease of biodiversity because of sepration we have a Genetic drift and some time population are in bottle neck situation so they have to inbreeding and decreasing Gene diversity, and finally rich ness is decrease too and all thing that I say lead to decrease biodiversity

I hope to said a obvious answer

good luck

Fragmentation in most cases decreases biodiversity. We have to point that the process of energy transferences, generaly, are affected by the habitat fragmentation. I have conducted some studies in aquatic systems. The results also pointed the fragmentation as cause os changes in the invertebrates communtiy structure. The River continnum concept (RCC) give some ideas about this issue. Best regards.

yes, I agree. Even if in a first moment in very specific situations someone can observe any increase... overtime it's not what happens.

My suspicion is that the window of observation covered by ecologial studies of extant biota is too small (in terms of time and space) to decline the hypothesis that some (e.g. slow, long term) processes of habitat fragmentation lead to an increase in biodiversity.

What we can observe today are merely short term processes biased by human intervention... so without fossil data there is probably no chance to get a more general answer.

Over evolutionary time, fragmentation can increase rates of both speciation and extinction. I hate to sell my own work, but have a look at Lineages that Cheat Death in Evolution, which addressed some diversification consequences of populations that become isolated in small areas.

Over ecological time, it is also important to note that if fragmentation creates a richer mosaic of habitat types than before, than it can increase beta diversity and thus gamma diversity. The final answer will very much depend on the degree of fragmentation, the size of the remaining fragments, and the difference in habitat variety between the former land coverage and the newer mosaic. There are various pieces of work on this by Teja Tscharntke and of course suggestions about it from classic fragmentation researchers such as Lenore Fahrig. You can also google Intermediate Disturbance Hypothesis to get a line of thought related to this question.

The key question for ecologists, however, is not how many species are found in the fragmented habitat. Rather, they should ask which species: is there an influx of generalists and an impoverishment of functional groups? This consideration affects the evolutionary answer. A landscape that is so heavily fragmented that only vagile generalists are left is unlikely to generate speciation because the survivors are unlikely to establish reproductive isolation.

I think habitat fragmentation is a temporal and spatial process. Assessment of its impact is influenced hugely where and at which phase of the process the habitat was investigated. To answer this question series of long term studies are needed. There are great differences among habitats and fragmentation processes. Our assessment possibility is limited as well as ecological knowledge.

It is a matter of specific ranges and of relative observations about diversity of food webs. Often it is in narrow sense a loss of function that is impaired more that a loss in the number of species. This would be reflected by changes in some web component like litter, water purity and carbon stock. The diversity in these terms is a complex table of cycles efffciciency under diffrent fragmentations.

Hi Robert

Reports indicate that loss of habitat exerts substantial negative impacts on biodiversity in a region. While, I think, habitat fragmentation as such may have either positive or negative influence on the biodiversity. It all depends on the left over size of the populations in the community after the phenomenon of habitat fragmentation. It is important that the impacts of these two processes (habitat loss & fragmentation) be appraised separately.

Best

Dola

As most things in ecology, it is incredibly difficult to build a general rule in my opinion. I believe it is highly dependent upon the extent of the fragmentation (ie "gaps" among habitat patches), the geometry among the remaining habitat patches, and the relative dispersal/movement capabilities of the biota within habitats.

While edge habitats tend to exhibit increased predation, they do allow for opportunistic/generalist or even species better suited for edges to exist (this obviously might not be the case in extreme examples, ie when an "edge" is a building/city), which can increase biodiversity. If the edge habitat to non-edge habitat ratio is too high, however, you can start to impose density-dependent processes on biota that is unable to successfully disperse among patches. This is also true of fragmentation characterized by "wide edges" (clear-cut forests for example).

Another way to think of the situation is thinking of habitat fragmentation as a specialized case of disturbance. Often, intermediate levels of disturbance are correlated with increased biodiversity relative to very low levels of disturbance. However, high levels of disturbance can definitely have negative and long-lasting impacts on biodiversity. The effect on biodiversity again depends on the relative size of the disturbance relative to the ecosystem/habitat patch area, it's ability to immediately impact biota, and how much it impedes movements of biota.

In short, narrow and non-contiguous edges might increase biodiversity. Unfortunately, much of anthropogenic fragmentation results in highly-fragmented landscapes with small remaining habitat patches and large gaps among (as well as highly dangerous gaps - such as roads) that will generally result in decreased biodiversity.

”Does habitat fragmentation increase ... biodiversity? ”

Yes, if the ”habitat” is an agri-monoculture

Test

My opinion is that influence depends on the scale. When fragmentation creates coarse-grained mosaic, diversity may win and became enhanced. When fragmentation breaks habitat into very small parcels (fine-grained mosaic), diversity is supressed.

Secondly, much is dependent on the corridors between patches.

Third, whak kind of organisms we are speaking about, and what geographical latitude / biome we are considering? In the south, tropical habitats are fragmented by nature. In the North, fragmentation is much bigger trouble.

Robert, I agree with Linas' comments. Scale/grain is very important, as are the number and size of the corridors, what organisms are you interested in - and also length of time to measure diversity. My work on tropical butterflies suggests that species abundance distributions are strongly affected by disturbances (large and small). Generally species in disturbed forest are more abundant than an intact forest with the same underlying community of species. Measuring tropical forest butterfly diversity requires long-term studies, particularly in forests with little disturbance. There are no rapid methods, and few really solid data-sets. As in much of ecology and diversity work, it is a sampling problem in space and time. As you are working in Bolivia, I am attaching a few papers that might (or might not) be of use to your work/questions. Phil

Sorry are are 2 others

i need to learn how to use RG! heere is the last one

Agreed with Linas' answer. Type of organism, existing corridors and size of fragmentation is important as mentioned by Linas. In my opinion beside these three kind of fragmentation, whether it is natural isolation or human-induced also make a difference. If it is land transformation by human then local extinction of species is likely but the occurrence of speciation process and increase in biodiversity is unlikely. I think such kind of fragmentation does not pressurize population to adopt in new environmental setting, both isolated populations are continuing to live in an environmental setting in which they are adapted to live in. In contrast to human induced fragmentation, if isolation was caused by some environmental change, (e.g. Shift in climate zone, geological changes) which take a long period to happen speciation is likely to occur hence increasing number of biodiversity. Here also need to consider two aspects (1) species genetically adapting capacity in an evolutionary process, or (2) physiological plasticity in species (see Austin & Moehring, 2013). Plasticity help species to adopt in new environmental setting hence no speciation occurs and when isolated populations came closer they can exchange genetic information easily (see Jain, A., Pandit, M. K., Elahi, S., Jain, A., Bhaskar, A., & Kumar, V. (2000). Reproductive behaviour and genetic variability in geographically isolated populations of Rhododendron arboreum (Ericaceae). Current Science, 79(9), 1377–1381).

It is hard to talk about biodiversity as such. Most investigations deal with a group of animals or plants. For example, effect of fragmentation on large carnivores.

Then, in animals not only grainof fragmentation, but also size (as a proxy of mobility) matters. For small mammals we are talking about fragmentation with mosaic measured in hectares or sq. kilometers, but for large ungulates or carnivores - by hundreds/thousands of sq. kilometers.

To switch from fragmentation to speciation - not easy; logically we suppose, that fragmentation appeared and continue to exist, but the smaller the grain, the less are chances to know fragmentation history. Thus, I suppose, there is no exact answer to the original question, just theories.

Regarding scale, please read the explaining text below my question. And as well the reviews provided by some contributors, making some answers here redundant.

Zsolt and Sailesh, I am not talking about transformation and habitat loss, I have actually seen human impact that might be in the scale of natural forest succession processes. However, my fault, the intial title of my question was misleading and provocative.

Phil, you should take into account that fruit feeding butterflies are an evolutionary trait requiring fruit trees and that will necessarily show low diversity in a forest succession. When you however additionally take into account butterflies feeding on vascular plants, usually occurring on forest successions, e.g. on a landslide or riparian habitat (all fragmentation), you will get much higher butterfly diversity than in an “intact” stand including fruit trees. Same thing with tiger beetles, diversity of arboreal species is highest in forest, however, there are other non-forest traits contributing to diversity of this group.

Do we tend to consider human impact in generally harmful for forest diversity? Here I can see some bias, however, also some good answers (to my poor question).

Agree with most comments. Increases or decreases in diversity in fragmented forests habitat can be very much depend on type of organisms you choose as your model research study and size of fragmented forests (Benedick et al 2007). For example, sun loving species of butterflies may be less effected by forest fragmentation as compared to other organisms such as nocturnal moths which in turn may reflect your findings. Benedict et al (2007) found that there were very little differences in terms of alpha diversity between smaller and larger sizes of fragmented forests for fruit feeding butterflies. However, as compared to larger forest fragments, smaller and isolated forests tend to contain many species with little conservation value such as restricted geographical ranges / endemic and restricted ecological requirements. My recent finding (unpublished), found that marked differences in diversity of nocturnal moths between smaller and greater fragmented forests; lower alpha diversity in smaller and isolated forest fragments which is contradict to previous butterflies research....

Hope this answer useful...

Useful answer and references.

Looking for "Intermediate Disturbance Hypothesis" might bring some additional insights, however, the hypothesis remains controversal.

Intermediate disturbance may be useful for studies related to logging or RIL. Fragmentation favor speciation as well remain speculative because how the remaining species respond to it are usually very little known. Buffer zone seems ideal to reduce edge effect and other type of disturbance from the surrounding area and I agree with Robert on this. But whether most agricultural companies agree to have forest within their plantation area is another issue. In terms of genetic diversity, for example Benedick et all 2007 showed recent fragmentation - 100 years below seems to have little effect on species that were capable to adapt in all fragmented forests. Sad things is, those of narrow habitat species such endemic were already gone as soon the forest become fragmented and isolated. Perhaps we could try to choose species that are available in all forest fragments but as well highly sensitive to habitat disturbance if we were really want to try to get better picture on how they might respond to fragmentation.

Suzan, agreed.

Sailesh, I would like to discuss your answer, because you are one of the few addressing the aspect of allopatric speciation, highly appreciated.

I think we have to distinguish between (1) the invading of corridors by already existing species, which is certainly supposed by the most here when talking about an increase of diversity, if at all, and (2) an increase of diversity by allopatric speciation in both, the forest species and species invading the corridors, fostered by dispersal barriers (corridor and forest).

As already mentioned in my question I have excluded the possibility of land transformation, habitat loss and species extinction (“What happens if fragment size remains unchanged and sub-populations persist? “).

Your point: “both isolated populations are continuing to live in an environmental setting in which they are adapted to live in.”

I think it’s very unlikely that the established fragments will be identical.

“In contrast to human induced fragmentation, if isolation was caused by some environmental change, (e.g. Shift in climate zone, geological changes) which take a long period to happen speciation is likely to occur hence increasing number of biodiversity.”

That’s exactly the point I was addressing in my question. Why are you talking about shifts on a continental scale? There are heterogeneous habitats within a spatially small scale (e.g. in the Andes) and regularly occurring perturbations in forest such as falling trees and deer passes that could be considered as fragmentation and that are assumed to have considerably increased diversity by creating different microhabitats with varying radiation, humidity, etc.

Human impact is not automatically land transformation such as in the European area, it starts with hunting monkeys in the Amazon forest or keeping cattle in a transhumance system, without burning forest. Fortunately many people e.g. in Bolivia dont have the technical possibilities for industrial logging or agriculture.

However, it makes a big difference to the subsistence farmers living along the borders of forests if conservation biologists and decision makers consider their activities as threats for forest or as comparable with natural succession processes (that are even assumed to increase diversity). Well, in some countries decision makers have recognized this problem and have created buffer zones with restricted human activities. However, I think it is not really clear what happens in such buffer zones, even assumed the people there keep their activities to a minimum.

On a global scale, human presence will at least cause fragmentation. The answer of my question would make a big difference for our sense of self. Okay, I know, it depends on the scale...

Rober, agreed. Forest fragmentation caused by human is a recent disturbance and it is indeed very different from natural / geological disturbance (etc. mention by Robert). In Borneo, many forests generally surrounded by large scale of oil palm plantations and these fragments may be important for the conservation of many organisms as they may potentially support many species of high conservation value (not only insects). In case of fruit feeding butterflies in Sabah, many species particularly narrow geographical ranges, are not able to make use of more degraded forest and were more adversely affected by forest fragmentation. Thus protection and management of these forests will probably help to reduce current extinction rates. Forests in Sabah is protected by Sabah Forestry Department which I think could minimise antropogenic disturbance. However...there still need more work to be done...such as enforcing strict law, educating farmers and etc.

An accepted goal of conservation is to build a conservation network that is resilient to fragmentation and environmental change. However, fragmentation is a relative concept as well as connectivity. Effective corridors should provide suitable and reliable connectivity among habitats across scales for species mobile or less mobile for gene exchange under uncertainty and change. However, often a "static" vision of landscapes is adopted (i.e. the cartography of land uses/covers) whereas landscapes (habitats included) are dynamic. Indeed, they do change either under different seasonal conditions, or under multiple driving forces like, for instance, climate change. As a result, what we are looking for, i.e. fragmentation or effective corridors, can systematically change on the map, and what is fragmented or suitable as corridor under certain conditions could not be suitable or fragmented when season, conditions or the set of focal species are changed. Just because we are not so good in predicting the future and what could be a suitable network sustaining biological diversity and gene exchange, we have to rely on past time series (at a suitable scale) to define the trajectory of every landscape piece to see whether it is predictable or not, that is, if it is persistent or not. Once you get a "predictability" map then you can think of applying different modelling tools to derive, under uncertainty; what possibly could be an effective corridor network and a suitable fragmentation for the future. So you could discover that along with "classical" green and blue ways other elements in the landscape could be crucial for the network based on their predictability. You could also discover which unpredictable landscape pieces are crucial for the maintenance of the overall connectivity in the face of climate change and try to transform them in "persistent" through planning and management efforts. See, for instance, the paper "Highlighting order and disorder in social–ecological landscapes to foster adaptive capacity and sustainability" recently appeared in Landscape Ecology.

The same principle should be applied to fragmentation/connectivity for marine systems (see Modeling population connectivity by ocean currents, a graph-theoretic approach for marine conservation appeared in Landscape Ecology). Indeed, for many marine species, population connectivity is determined largely by ocean currents transporting larvae and juveniles between distant patches of suitable habitat. So, connectivity relies on the persistence of ocean currents suggesting areas that might be prioritized for marine conservation efforts and that are working like "stepping stones" in the maintenance of the overall network. On the other hand, you might identify "new" candidate stepping stone areas in case of predicted changes in the oceanic current pattern due to climate change. Unfortunately most of marine biologists and ecologists involved in marine conservation do not consider the importance of ocean currents.

Sounds reasonable to me.

However, "Effective corridors should provide suitable and reliable connectivity among habitats across scales for species mobile or less mobile for gene exchange under uncertainty and change."

Is connectivity a precondition for survival of the sub-populations? Maybe, references would be highly appreciated, but if not, why should be connectivity provided? I would recommend the opposite!

Likely because of lacking connectivity due to disconnected sea currents I was allowed to discover and describe a new land crab species (with pelagic larvae) endemic to Cocos Island. Diversity in this genus increased from four to five species.

I can say in the binging of fragmentation there will be decrease in biodiversity, but with time we can expect to increase biodiversity, provided suitable environmental conditions.

For my mind, i think fragmentation is a process that surely has an influence on biodiversity. This influence depend on the size of fragment and a type of concerned biodiversity.

We have to consider the type of diversity we talk about : animal ; vegetal (trees or grass), marine…

So, we can’t absolutely take only one way by saying fragmentation increase or decrease biobiversity but what we are sure,it remodelates structure and componant of habitat.

In the case of Forest for example, Habitat fragmentation reduces total forest area and increases of the number of forest patches; it constitutes one of the major threats for biodiversity because many species depend on the specific microclimatic and ecological conditions of forests to complete their life cycle or a part of it, and cannot survive without our outside these particular environments.

This material should give some insight on the subject.

And this too should be of help. Cheers.

Regarding the specialization of populations we have shown that over a relative short time of 100 years you can identify different sub-populations of Moor frog (Rana arvalis)... More specifically, you can relate the rate of isolation with the landscape history, the moment that populations we cut off from the larger populations. In species like amphibians that go frequently through bottlenecks as a result of environmental variability or pressures, this specialization can go rapidly.

However, in such time frame no sub-species are formed of course.

I agree with Giovanni that indeed building a network is most important for mainting (restoring) biodiversity.

An interesting publication on the SLOSS debate, and in particular large areas versus landscape connectivity, is the paper from Schippers et al.: it shows that landscape connectivity is often more important than increasing areas.

It underlines the importance of a varied landscape, a matrix with larger areas with smaller, connecting landscape elements to ensure landscape connectivity.

So yes, decreasing fragmentation is beneficial for biodiversity, as shown in this paper.

Article Genetic population differentiation and connectivity among fr...

and, the paper of Schippers et al. 2009....

Article Sacrificing patches for linear habitat elements enhances met...

Theo, the first part and the conclusion of your post and as well the attached paper you have co-authored are contradictory. The habitat fragmentation analyzed by Shipper et al. (10% remaining woodland) is habitat loss to me. You dont eat 90% to cut a cake. please take into account that there are less fragmented woodlands in the world than the continent Europa. Already said above.

Moderate disturbances are known to increase biodiversity. Fragmentation, if amounts to such disturbance will be beneficial for the biodiversity, irrespective of the former floral and faunal elements in the ecosystem, as we ought to remember that fragmentation will always threaten the existence of sensitive species, especially mammals.

Robert,

I agree that both situations I cite are from the 'old continent' Europe, and in particular the Netherlands, or in the case of the paper from Schippers, based on fragmented landscapes and parameters for Western Europe. This is a severely fragmented situation, due indeed to habitat loss.

But, such fragmented landscapes also occur in Africa. I observed that most of the Guinean forest hotspot, (in Ghana only at most 11% remains, overall only 15% is remaining according to CI), and I'm sure also in Russia or various areas in Brasil, the same rate of fragmentation occurs. So it is not specific for Europe, and probably the more common condition for nature.

You add indeed in your introduction that the fragment size does not remain the same, due to habitat loss. Even in the case that it remains the same in physical size as you assume, we must be aware that habitat quality (or carrying capacity) often declines due to factors such as climate change or succession, landscapes are rather dynamic. Therefore, the corridors are essential to maintain the metapopulations under these conditions, to allow the migration of species and expansion of the range -although the expansion rate is perhaps limited, in the light of the rapid climate change.

Whether habitat fragmentation can increase or decrease biodiversity should be seen from different perspectives: Over time and space, degree of fragmentation (distance between patches of habitats), natural and anthropogenic disturbances (climate change, overexploitation, etc.), resilience of ecosystems, and so on. Habitat fragmentation has relative disadvantages and advantages. In many cases, habitat fragmentation affects the fabric of ecosystem elements/members, decreases gene flow, disrupts species interactions and reduces ecosystem productivity, among others. More isolated patches of habitats receive higher impacts than proximate patches. On the other hand, habitat fragmentation and isolation can increase diversity by shaping evolution and speciation. Allopatric speciation occurs basically due to geographical isolation and thus reproductive isolation. Moreover, diversity across landscapes is the result of discontinuities in environmental conditions and modifications by humans (many landscapes are cultural landscapes). But it is important to note that the negative impacts of habitat fragmentation and loss outweigh the positive impacts. Thus, conservation efforts are needed to decrease habitat fragmentation and loss in the face of human population growth and natural calamities such as climate change.

From my point of view i believe that whether habitat fragmentation will affect or not will be determined by the habitat range of the local fauna. If the agent of fragmentation does not intercept or interrupt the habitat range, the diversity may remain relatively undisturbed, unlike otherwise where species interactions and access to niches will disturbed.

In my opinion,in general, the fragmentation initially increases the diversity with both Intermediate Disturbance Hypothesis and also with Ecotone effect and then decreases.

https://www.researchgate.net/publication/301609558_Geospatial_analysis_of_forest_fragmentation_in_Uttara_Kannada_District_India

Article Geospatial analysis of forest fragmentation in Uttara Kannad...