Such swings have major implications for forestry-reliant rural economies. Some of the changes in forest sector activity could be gradual; others could be sudden and dramatic—as the mountain pine beetle outbreak has shown.
Explicit Not Implicit Preferences Predict Conservation Intentions for Endangered Species and Biomes
The extensive and relatively fast mortality caused by the beetle infestation has led to short-term increases in timber supply while the beetle-killed wood is salvaged. However, once that wood runs out, the annual harvest is expected to decline significantly. Another concern is that a warming trend could reduce the season and limit the use of winter roads in regions where winter forestry operations are the norm in Canada. For example:.
The decision-making context for forest management will be increasingly complex and uncertain. Yes, forest management activities such as harvesting, tree planting, and efforts to fight forest fires and insects have an impact on the forest carbon balance. In some cases, suppression of fires and protection against insects can lead to a reduction in the area affected and help maintain the carbon stored; however, our ability to reduce fire and insect impacts on carbon in the long term or over large landscapes is uncertain.
Harvesting results in large losses of carbon from the forest in the short term, but the regeneration of the trees then takes up large amounts of carbon. As well, much of the harvested carbon is stored for a long time in forest products that society needs. Addressing the challenges brought on by climate change will require forest managers to be more flexible, more forward looking and more adaptable than ever before. And, if they are to meet these responsibilities effectively, forest managers will also be relying more than ever on better monitoring and decision support.
Action taken over the next few decades will determine how impoverished the biosphere will be in 1, years when many species will suffer reduced evolvability and require interventionist genetic and ecological management. Whether the biota will continue to provide the dependable ecological services humans take for granted is less clear. The discussants offered recommendations, including two of paramount importance concerning human populations and education , seven identifying specific scientific activities to better equip us for stewardship of the processes of evolution, and one suggesting that such stewardship is now our responsibility.
The ultimate test of evolutionary biology as a science is not whether it solves the riddles of the past but rather whether it enables us to manage the future of the biosphere. Our inability to make clearer predictions about the future of evolution has serious consequences for both biodiversity and humanity. The science of evolution, linked to the related sciences of ecology, paleobiology, and genetics, seeks to explain the history of life on earth.
After about years of formal inquiry, we seem to be more than half way to accounting for the development of biomes and biotas, the biosphere, and ourselves. We can now account for much of the past and present in terms of genetics, ecology, and chance. However, the real measure of a science's maturity is its ability to make sound predictions about the future. Our discussion of the future of biomes and biotas, even with one of the colloquium organizer's contributions 1 — 3 as a guide, revealed that we are frankly unequal to this challenge despite its urgency.
Our inability to make clear predictions beyond sweeping generalizations about the future of life on earth has serious consequences for both biodiversity and the well being of humanity.
If our greatest achievement in the last century was the collective understanding of what evolution and its products, the biosphere, mean to our own survival, the challenge of the present century is to develop a more predictive science of evolutionary ecology before it is too late to shape a desirable future. There is no doubt that the biodiversity crisis is real, and upon us, and began roughly 30, years ago 8.
We speak with less scientific assurance, however, about almost every one of the widely quoted numbers describing its magnitude and significance. Nevertheless, we live at a geological instant when global rates of extinction are at an all time high for the last 65 million years My and are increasing. Most extinctions go unrecognized; thus, estimates of overall rates have high errors.
Probably at least , species went extinct in the last century, and 10—20 times that many are expected to disappear this century. Although we can identify the most threatened biomes and species in some groups [ref. The taxonomic course of the biodiversity crisis is reasonably understood for terrestrial vertebrates and a few other groups In the last few centuries, we have lost one family of mammals Nesophontidae , half the birds of Hawaii, possibly the most common bird in North America the passenger pigeon , and all of the moas—a total of 1, documented plant and animal species globally.
Further, we have extirpated most of the fish in the lakes of the northeastern United States and most of the primates from the remaining forests of West Africa. The situation in the oceans is poorly known but comparable or worse If we step back 30, years, we have contributed to the elimination of the megafauna of the Holarctic, Neotropics, and Australian zoogeographic regions 70 species and 19 genera of mammals in North America ; these extinctions involve the disappearance of several other families of mammals Today's taxon-specific global extinction rate estimates are 50— times background, and half the remaining vertebrates are at risk of extinction, including most whales and primates.
Taxon-specific assessments of threat have been prepared by the Conservation Breeding Specialist Group of the World Conservation Union IUCN for many groups ranging from palms to parrots to Papilio , the swallowtail butterflies. This claim can be made, because in most genera, there are several species, and the survival of one, it is argued, may capture most of the genetic variability of the whole clade. Although this estimate is controversial, it explains why some question whether we should be saving rare species in species-rich clades.
Is one tuatara worth species of skinks? Are rare species treasures or dross 15 from an evolutionary point of view? However, saving phylogenetic diversity is not currently the goal of global conservation efforts, and science does not yet clearly indicate that it should be. The ecological consequences of our destruction of biomes and biotas are understood in broad generality as they impact human well being locally and regionally.
Less clear are the global implications of habitat destruction, especially species-rich tropical forests, wetlands, and coral reefs Predictions are complicated further by the recent realization that human activities are altering climates globally. The exploration of Sala and coworkers 17 , 18 of the impact of various drivers of change and the interactions between these drivers on global ecosystems and biodiversity loss in the year illustrates both the power and the current limitations of scientific inquiry at this level of concern.
Nevertheless, there is general agreement that the biosphere will have fewer species and be subject to more weed, pest, and disease outbreaks. Heretofore dependable nutrient cycles may become less predictable as essential microbes succumb to anthropogenic toxins.
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The new biomes will be more easily disturbed and invaded, and will have an aesthetically unappealing dullness. In considering these generalities, the discussants agreed on one thing: evolution will continue as the major driver or cause of biodiversity. Although we are ushering in a period of geological time characterized by the homogenization of biotas 19 , 20 , dubbed the Homogecene at this meeting, the basic processes causing evolution will continue. Evolution is not over—set back perhaps—but by no means over. There was, however, surprising debate as to whether it warrants being called a mass extinction event.
This difference of opinion is both important and potentially dangerous. Mass extinction events are typically defined in terms of their irreversible impact on large numbers of species in diverse taxa on a global scale in a short period. Thus, attempts to show the magnitude of the current extinction event on a plot of marine invertebrate families is inappropriate and dangerous in that it belittles its significance.
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Unfortunately, the comparable multitaxon plot of species numbers through time is not yet available; when it is, we will be able to illustrate graphically the probable impact of the current event in comparison with the previous big five marine invertebrate mass extinctions. A hint of what this impact might look like is provided by Alroy's studies of North American mammal species through the last 98 My Regan et al.
My personal opinion is that we are currently living in what will eventually be recognized as a real mass extinction. Furthermore, extinctions do not occur at random in space and in clades. Purves et al. The authors estimate that an additional genera of mammals and birds are at risk over expectations under random extinctions.
What Are the Impacts of Humans on Grassland Biomes? | Sciencing
Regardless of whether such calculations qualify the current biodiversity crisis as a mass extinction event, we all agreed that it would be inexcusable to let it become one or a worse one. To this end, we reached conclusions that may be summarized here as: arm the scientists, alert the public, and do anything to buy time. The causes of the biodiversity crisis are well known and include human impacts on habitats habitat destruction, degradation, fragmentation, and restructuring and on organisms overexploitation, introduction of exotic competitors, predators and parasites, and creating new pests 8 , 10 , 31 , Discussants noted differences in geographic rates of habitat alteration and destruction largely complete in Europe and North America and on-going in the tropics and that such rates are unprecedented in the tropics and subtropics in the Neogene.
There was agreement that community simplification with loss of pollinators and dispersers and the regional homogenization of biotas, with weedy opportunists replacing endemic specialists, are of serious concern. The well recognized vulnerability of island biotas will be exacerbated by our accelerated importation of parasites and predators.
Potential threats from transgenic genetically modified organisms will require vigilance and careful assessment In coinciding with a period of rapid anthropogenic global warming, the biodiversity crisis could not have come at a worse time.
The rate of warming is unusually fast but not without precedent Orbitally forced species range dynamics associated with ,year Milankovich cycles have caused repeated changes in the distributions of most temperate zone species 37 , 38 and caused ranges of some North American species to shrink progressively with successive cycles The ability of species to respond to future climatic oscillations by range shifts will be greatly reduced by our creation of an inhospitable matrix between the remaining habitat patches.
Increased nitrogen will also have significant impacts on soils, plant productivity, and biodiversity The first assumption concerns human numbers and provides a simple metric of the impact of our population. The second assumption concerns our per capita consumption of natural resources, food, and energy. Discussion of the future of evolution presupposes the availability of acceptable year and 1,year projections for human populations. Not surprisingly, the 1,year projections for human numbers and behavior are too speculative to print; however, it is already clear that we cannot expect a return to a prebiodiversity crisis state of nature under even the most favorable scenarios with reduced human impact.
Recovery from previous mass extinction events has taken 5—10 My 41 , Action taken in the next few decades will determine how impoverished the biosphere will be in 1, years. One of the lessons of paleobiology is that a species geographic range is a good indicator of its probability of surviving mass extinction events, ice ages, and other major environmental changes see refs.
In the past, single species and interacting species have moved rather than adapted to such change, but such dispersal will no longer be possible. In future, terrestrial species will have to adapt or their dispersal will have to be managed, especially in plants and other low-vagility organisms. Ironically, this realization comes just as progress is being made on one of the great puzzles of the Modern Synthesis, the evolution of species ranges 44 , on how climate change leads to both local adaptation in peripheral populations and range shifts Gene flow is predicted to increase in commensal species and decrease in natives as their ranges become fragmented.
Spatial heterogeneity will therefore decrease in commensals and increase in natives. Templeton 46 argues that range fragmentation will lead to extinction and not speciation, because the individuals in fragmented populations will not increase in numbers fast enough for divergence to occur.
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Managers will have to move the proverbial one individual per generation between remnant subpopulations of metapopulations to counter genetic drift The possibility that habitat fragmentation may actually increase rather than decrease gene flow and population genetic variation, as found recently in Acer 48 , needs further examination.
Studies of probable adaptive responses of individual species to global warming are in their infancy e. Although the ecological and behavioral characteristics associated with high extinction risk are reasonably well understood but only in a few taxa , the population genetic components of viability are also receiving attention Genetic drift is expected to decrease in the growing populations of commensals and increase in the fragmented and smaller populations of natives. Genetic risks that were largely ignored in the last century will become dominant concerns in a world of small, recently isolated populations with declining genetic effective population sizes, N e.
Genetic erosion, the decrease in population variation caused by random genetic drift and inbreeding, is both a symptom and a cause of endangerment of small isolated populations Recently, a method for monitoring genetic erosion based on noninvasive genotyping using nuclear microsatellite variation has been introduced Our studies showed that, although genetic erosion accompanied habitat fragmentation and demographic collapse in some species, the process apparently can begin before detectable demographic decline of local populations of other species This finding is important, because genetic studies of threatened populations usually are performed only after demographic studies indicate that there is a problem.
In the future, managers will have to survey both demography and genetics, and their interaction, to assess a fragmented population's viability. In addition to genetic drift, inbreeding can also threaten a fragmented population's viability 53 , and again, recent application of molecular genetic assays provides a clear demonstration of its impact on extinction in nature The implication of these observations is that wildlife managers will increasingly have to intervene; nature can no longer be left alone to function, because our actions have doomed countless isolated populations to slow genetic decline and extirpation.
The threats of genetic swamping of rare species by common congeners are seen as increasing Molecular genetic methods now permit the detection of earlier incidents of genetic assimilation that have extirpated or exterminated one of the hybridizing taxa. The assimilated taxon remains as a phantom in the gene pool of the surviving species whose variability is enhanced by the interaction. Whether this increased variability increases its evolvability is not known, but it may. Existing theory does not give a clear general answer.
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