Habitat type determines herbivory controls over CO2 fluxes in a warmer Arctic

High-latitude ecosystems store large amounts of carbon (C); however, the C storage of these ecosystems is under threat from both climate warming and increased levels of herbivory. In this study we examined the combined role of herbivores and climate warming as drivers of CO2 fluxes in two typical high-latitude habitats (mesic heath and wet meadow). We hypothesized that both herbivory and climate warming would reduce the C sink strength of Arctic tundra through their combined effects on plant biomass and gross ecosystem photosynthesis and on decomposition rates and the abiotic environment. To test this hypothesis we employed experimental warming (via International Tundra Experiment [ITEX] chambers) and grazing (via captive Barnacle Geese) in a three-year factorial field experiment. Ecosystem CO2 fluxes (net ecosystem exchange of CO2, ecosystem respiration, and gross ecosystem photosynthesis) were measured in all treatments at varying intensity over the three growing seasons to capture the impact of the treatments on a range of temporal scales (diurnal, seasonal, and interannual). Grazing and warming treatments had markedly different effects on CO2 fluxes in the two tundra habitats. Grazing caused a strong reduction in CO2 assimilation in the wet meadow, while warming reduced CO2 efflux from the mesic heath. Treatment effects on net ecosystem exchange largely derived from the modification of gross ecosystem photosynthesis rather than ecosystem respiration. In this study we have demonstrated that on the habitat scale, grazing by geese is a strong driver of net ecosystem exchange of CO2, with the potential to reduce the CO2 sink strength of Arctic ecosystems. Our results highlight that the large reduction in plant biomass due to goose grazing in the Arctic noted in several studies can alter the C balance of wet tundra ecosystems. We conclude that herbivory will modulate direct climate warming responses of Arctic tundra with implications for the ecosystem C balance; however, the magnitude and direction of the response will be habitat-specific.     

Antagonistic effect of natural habitat conversion on community adjustment to climate warming in nonbreeding waterbirds

Although the impacts of climate and land-use changes on biodiversity have been widely documented, their joint effects remain poorly understood. We evaluated how nonbreeding waterbird communities adjust to climate warming along a gradient of land-use change. Using midwinter waterbird counts (132 species) at 164 major nonbreeding sites in 22 Mediterranean countries, we assessed the changes in species composition from 1991 to 2010, relative to thermal niche position and breadth, in response to regional and local winter temperature anomalies and conversion of natural habitats. We observed a low-level, nonsignificant community adjustment to the temperature increase where natural habitat conversion occurred. At the sites affected by natural habitat conversion, the relative increase of warm-dwelling species in response to climate warming was 6 times lower and the relative species decline was 3 times higher than in the sites without natural habitat conversion. We found no evidence of community adjustment to climate warming when natural habitat conversion was >5% over 15 years. This strong negative effect suggests an antagonistic interaction between climate warming and habitat change. These results underline the importance of habitat conservation in community adjustment to climate warming.     

Tropical amphibians in shifting thermal landscapes under land‐use and climate change

Land‐cover and climate change are both expected to alter species distributions and contribute to future biodiversity loss. However, the combined effects of land‐cover and climate change on assemblages, especially at the landscape scale, remain understudied. Lowland tropical amphibians may be particularly susceptible to changes in land cover and climate warming because many species have narrow thermal safety margins resulting from air and body temperatures that are close to their critical thermal maxima (CT_max). We examined how changing thermal landscapes may alter the area of thermally suitable habitat (TSH) for tropical amphibians. We measured microclimates in 6 land‐cover types and CT_max of 16 frog species in lowland northeastern Costa Rica. We used a biophysical model to estimate core body temperatures of frogs exposed to habitat‐specific microclimates while accounting for evaporative cooling and behavior. Thermally suitable habitat area was estimated as the portion of the landscape where species CT_max exceeded their habitat‐specific maximum body temperatures. We projected changes in TSH area 80 years into the future as a function of land‐cover change only, climate change only, and combinations of land‐cover and climate‐change scenarios representing low and moderate rates of change. Projected decreases in TSH area ranged from 16% under low emissions and reduced forest loss to 30% under moderate emissions and business‐as‐usual land‐cover change. Under a moderate emissions scenario (A1B), climate change alone contributed to 1.7‐ to 4.5‐fold greater losses in TSH area than land‐cover change only, suggesting that future decreases in TSH from climate change may outpace structural habitat loss. Forest‐restricted species had lower mean CT_max than species that occurred in altered habitats, indicating that thermal tolerances will likely shape assemblages in changing thermal landscapes. In the face of ongoing land‐cover and climate change, it will be critical to consider changing thermal landscapes in strategies to conserve ectotherm species.     

Multidecadal climate variability and climate interactions affect subalpine fire occurrence, western Colorado (USA)

This study investigates the influence of climatic variability on subalpine forest fire occurrence in western Colorado during the AD 1600-2003 period. Interannual and multidecadal relationships between fire occurrence and the El Ni?o Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) were examined, in addition to the effects of phase interactions among these oscillations. Fires occurred during short-term periods of significant drought and extreme cool (negative) phases of ENSO and PDO and during positive departures from mean AMO index. At longer time scales, fires exhibited 20-year periods of synchrony with the cool phase of the PDO, and 80-year periods of synchrony with extreme warm (positive) phases of the AMO. Years of combined positive AMO and negative ENSO and PDO phases represent "triple whammies" that significantly increased the occurrence of drought-induced fires. Fires were synchronous with this phase combination over 0-30 year periods and distinctly asynchronous with the opposite phase combination. Overall, because fires are synchronous at supra-annual to multidecadal time scales with warm AMO events, particularly when combined with cool ENSO and PDO phases, this suggests that we may be entering a qualitatively different fire regime in the next few decades due to the recent shift in 1998 to a likely long-term warm AMO phase. Although uncertainty remains regarding the effects of CO2-induced warming at regional scales, given the multidecadal persistence of the AMO there is mounting evidence that the recent shift to the positive phase of the AMO will promote higher fire frequencies in the region.     

Potential effects of climate change on ecosystem and tree species distribution in British Columbia

A new ecosystem-based climate envelope modeling approach was applied to assess potential climate change impacts on forest communities and tree species. Four orthogonal canonical discriminant functions were used to describe the realized climate space for British Columbia's ecosystems and to model portions of the realized niche space for tree species under current and predicted future climates. This conceptually simple model is capable of predicting species ranges at high spatial resolutions far beyond the study area, including outlying populations and southern range limits for many species. We analyzed how the realized climate space of current ecosystems changes in extent, elevation, and spatial distribution under climate change scenarios and evaluated the implications for potential tree species habitat. Tree species with their northern range limit in British Columbia gain potential habitat at a pace of at least 100 km per decade, common hardwoods appear to be generally unaffected by climate change, and some of the most important conifer species in British Columbia are expected to lose a large portion of their suitable habitat. The extent of spatial redistribution of realized climate space for ecosystems is considerable, with currently important sub-boreal and montane climate regions rapidly disappearing. Local predictions of changes to tree species frequencies were generated as a basis for systematic surveys of biological response to climate change.     

Global Warming, Human Population Pressure, and Viability of the World's Smallest Butterfly

Abstract:  The effects of climate change and habitat destruction and their interaction are likely to be the greatest challenge to animal and plant conservation in the twenty-first century. We used the world's smallest butterfly, the Sinai baton blue ( Pseudophilotes sinaicus ), as an exemplar of how global warming and human population pressures may act together to cause species extinctions. We mapped the entire global range of this butterfly and obtained extensive data on the intensity of livestock grazing. As with an increasing number of species, it is confined to a network of small habitat patches and is threatened both by indirect human-induced factors (global warming) and by the direct activities of humans (in this case, livestock grazing and collection of medicinal plants). In the absence of global warming, grazing, and plant collection, our model suggested that the butterfly will persist for at least 200 years. Above a threshold intensity of global warming, the chance of extinction accelerated rapidly, implying that there may be an annual average temperature, specific to each endangered species, above which extinction becomes very much more likely. By contrast, there was no such threshold of grazing pressure—the chance of extinction increased steadily with increasing grazing. The impact of grazing, however, decreased with higher levels of year-to-year variation in habitat quality. The effect of global warming did not depend on the future level of grazing, suggesting that the impacts of global warming and grazing are additive. If the areas of habitat patches individually fall below certain prescribed levels, the butterfly is likely to go extinct. Two patches were very important for persistence: if either were lost the species would probably go extinct. Our results have implications for the conservation management of all species whose habitats are at risk because of the direct activities of humans and in the longer term because of climate change.     

Long-term reactions of plants and macroinvertebrates to extreme floods in floodplain grasslands

Extreme summertime flood events are expected to become more frequent in European rivers due to climate change. In temperate areas, where winter floods are common, extreme floods occurring in summer, a period of high physiological activity, may seriously impact floodplain ecosystems. Here we report on the effects of the 2002 extreme summer flood on flora and fauna of the riverine grasslands of the Middle Elbe (Germany), comparing pre- and post-flooding data collected by identical methods. Plants, mollusks, and carabid beetles differed considerably in their response in terms of abundance and diversity. Plants and mollusks, displaying morphological and behavioral adaptations to flooding, showed higher survival rates than the carabid beetles, the adaptation strategies of which were mainly linked to life history. Our results illustrate the complexity of responses of floodplain organisms to extreme flood events. They demonstrate that the efficiency of resistance and resilience strategies is widely dependent on the mode of adaptation.     

气候变暖背景下森林土壤碳循环研究进展

由人类活动引起的温室效应以及由此造成的气候变暖对森林牛态系统的影响已引起人们的普遍关注.森林土壤碳循环作为全球碳循环的重要组成部分,是决定未来陆地牛物嘲表现为碳源/碳汇的关键环节,揭示这一作用对于准确理解全球变化背景下陆地生态系统碳循环过程具有重要的指导意义.本文主要通过论述影响土壤碳循环过程的5个方面(土壤呼吸、土壤微生物、土壤酶活性、凋落物输入与分解、土壤碳库),综述了近10 a来全球气候变暖对土壤碳循环过程的影响.近年来,尽管已开展了大量有关土壤碳循环对气候变暖的响应及反馈机制的研究,并取得了一定的成果,但研究结果仍然存在很大的不确定性.整合各种密切关联的全球变化现象,完善研究方法和实验手段,加强根际微生态系统碳循环过程与机理研究将是下一步研究的方向和重点.参70     

Modeling amphibian energetics, habitat suitability, and movements of western toads, Anaxyrus (=Bufo) boreas, across present and future landscapes

Effective conservation of amphibian populations requires the prediction of how amphibians use and move through a landscape. Amphibians are closely coupled to their physical environment. Thus an approach that uses the physiological attributes of amphibians, together with knowledge of their natural history, should be helpful. We used Niche Mapper™ to model the known movements and habitat use patterns of a population of Western toads (Anaxyrus (=Bufo) boreas) occupying forested habitats in southeastern Idaho. Niche Mapper uses first principles of environmental biophysics to combine features of topography, climate, land cover, and animal features to model microclimates and animal physiology and behavior across landscapes. Niche Mapper reproduced core body temperatures (T_c) and evaporation rates of live toads with average errors of 1.6 ± 0.4 °C and 0.8 ± 0.2 g/h, respectively. For four different habitat types, it reproduced similar mid-summer daily temperature patterns as those measured in the field and calculated evaporation rates (g/h) with an average error rate of 7.2 ± 5.5%. Sensitivity analyses indicate these errors do not significantly affect estimates of food consumption or activity. Using Niche Mapper we predicted the daily habitats used by free-ranging toads; our accuracy for female toads was greater than for male toads (74.2 ± 6.8% and 53.6 ± 15.8%, respectively), reflecting the stronger patterns of habitat selection among females. Using these changing to construct a cost surface, we also reconstructed movement paths that were consistent with field observations. The effect of climate warming on toads depends on the interaction of temperature and atmospheric moisture. If climate change occurs as predicted, results from Niche Mapper suggests that climate warming will increase the physiological cost of landscapes thereby limiting the activity for toads in different habitats.     

Meta-analysis: trophic level, habitat, and productivity shape the food web effects of resource subsidies

Studies of the effects of cross-habitat resource subsidies have been a feature of food web ecology over the past decade. To date, most studies have focused on demonstrating the magnitude of a subsidy or documenting its effect in the recipient habitat. Ecologists have yet to develop a satisfactory framework for predicting the magnitude of these effects. We used 115 data sets from 32 studies to compare consumer responses to resource subsidies across recipient habitat type, trophic level, and functional group. Changes in consumer density or biomass in response to subsidies were inconsistent across habitats, trophic, and functional groups. Responses in stream cobble bar and coastline habitats were larger than in other habitats. Contrary to expectation, the magnitude of consumer response was not affected by recipient habitat productivity or the ratio of productivity between donor and recipient habitats. However, consumer response was significantly related to the ratio of subsidy resources to equivalent resources in the recipient habitat. Broad contrasts in productivity are modified by subsidy type, vector, and the physical and biotic characteristics of both donor and recipient habitats. For this reason, the ratio of subsidy to equivalent resources is a more useful tool for predicting the possible effect of a subsidy than coarser contrasts of in situ productivity. The commonness of subsidy effects suggests that many ecosystems need to be studied as open systems.     

Marine reserve design: optimal size, habitats, species affinities, diversity, and ocean microclimate.

The design of marine reserves is complex and fraught with uncertainty. However, protection of critical habitat is of paramount importance for reserve design. We present a case study as an example of a reserve design based on fine-scale habitats, the affinities of exploited species to these habitats, adult mobility, and the physical forcing affecting the dynamics of the habitats. These factors and their interaction are integrated in an algorithm that determines the optimal size and location of a marine reserve for a set of 20 exploited species within five different habitats inside a large kelp forest in southern California. The result is a reserve that encompasses approximately 42% of the kelp forest. Our approach differs fundamentally from many other marine reserve siting methods in which goals of area, diversity, or biomass are targeted a priori. Rather, our method was developed to determine how large a reserve must be within a specific area to protect a self-sustaining assemblage of exploited species. The algorithm is applicable across different ecosystems, spatial scales, and for any number of species. The result is a reserve in which habitat value is optimized for a predetermined set of exploited species against the area left open to exploitation. The importance of fine-scale habitat definitions for the exploited species off La Jolla is exemplified by the spatial pattern of habitats and the stability of these habitats within the kelp forest, both of which appear to be determined by ocean microclimate.     

Phenology of mixed woody-herbaceous ecosystems following extreme events: net and differential responses

Ecosystem responses to key climate drivers are reflected in phenological dynamics such as the timing and degree of "green-up" that integrate responses over spatial scales from individual plants to ecosystems. This integration is clearest in ecosystems dominated by a single species or life form, such as seasonally dynamic grasslands or more temporally constant evergreen forests. Yet many ecosystems have substantial contribution of cover from both herbaceous and woody evergreen plants. Responses of mixed woody-herbaceous ecosystems to climate are of increasing concern due to their extensive nature, the potential for such systems to yield more complex responses than those dominated by a single life form, and projections that extreme climate and weather events will increase in frequency and intensity with global warming. We present responses of a mixed woody-herbaceous ecosystem type to an extreme event: regional-scale pi?on pine mortality following an extended drought and the subsequent herbaceous green-up following the first wet period after the drought. This example highlights how reductions in greenness of the slower, more stable evergreen woody component can rapidly be offset by increases associated with resources made available to the relatively more responsive herbaceous component. We hypothesize that such two-phase phenological responses to extreme events are characteristic of many mixed woody-herbaceous ecosystems.     

Processesof Tamarix invasion and floodplain development along the lower Green River, Utah.

Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century along many large floodplain rivers in the American Southwest. Native Populus forests have declined, while the exotic Eurasian shrub, Tamarix, has proliferated and now dominates most floodplain ecosystems. Photographs from late 19th and early 20th centuries illustrate wide river channels with largely bare in-channel landforms and shrubby higher channel margin floodplains. However, by the mid-20th century, floodplains supporting dense Tamarix stands had expanded, and river channels had narrowed. Along the lower Green River in eastern Utah, the causal mechanism of channel and floodplain changes remains ambiguous due to the confounding effects of climatically driven reductions in flood magnitude, river regulation by Flaming Gorge Dam, and Tamarix invasion. This study addressed whether Tamarix establishment and spread followed climate- or dam-induced reductions in annual peak flows or whether Tamarix was potentially a driver of floodplain changes. We aged 235 Tamarix and 57 Populus individuals, determined the hydrologic and geomorphic processes that controlled recruitment, identified the spatial relationships of germination sites within floodplain stratigraphic transects, and mapped woody riparian vegetation cohorts along three segments of the lower Green River. The oldest Tamarix established along several sampling reaches in 1938, and 1.50-2.25 m of alluvium has accreted above their germination surfaces. Nearly 90% of the Tamarix and Populus samples established during flood years that exceeded the 2.5-year recurrence interval. Recruitment was most common when large floods were followed by years with smaller peak flows. The majority of Tamarix establishment and Green River channel narrowing occurred long before river regulation by Flaming Gorge Dam. Tamarix initially colonized bare instream sand deposits (e.g., islands and bars), and most channel and floodplain changes followed the establishment of Tamarix. Our results suggest that Tamarix recruitment was triggered by large annual floods that were followed by years with lower peak flows, not by periods of low flow alone. Tamarix appears to have actively invaded floodplains, while Populus colonization has been limited. Thus, Tamarix invasion may have greatly influenced floodplain development and riparian vegetation composition along the lower Green River since the early 20th century.     

Prioritizing forest management actions to benefit marine habitats in data-poor regions

Land-use change is considered one of the greatest human threats to marine ecosystems globally. Given limited resources for conservation, we adapted and scaled up a spatially explicit, linked land–sea decision support tool using open access global geospatial data sets and software to inform the prioritization of future forest management interventions that can have the greatest benefit on marine conservation in Vanuatu. We leveraged and compared outputs from two global marine habitat maps to prioritize land areas for forest conservation and restoration that can maximize sediment retention, water quality, and healthy coastal/marine ecosystems. By combining the outputs obtained from both marine habitat maps, we incorporated elements unique to each and provided higher confidence in our prioritization results. Regardless of marine habitat data source, prioritized areas were mostly located in watersheds on the windward side of the large high islands, exposed to higher tropical rainfall, upstream from large sections of coral reef and seagrass habitats, and thus vulnerable to human-driven land use change. Forest protection and restoration in these areas will serve to maintain clean water and healthy, productive habitats through sediment retention, supporting the wellbeing of neighboring communities. The nationwide application of this linked land–sea tool can help managers prioritize watershed-based management actions based on quantitative synergies and trade-offs across terrestrial and marine ecosystems in data-poor regions. The framework developed here will guide the implementation of ridge-to-reef management across the Pacific region and beyond.     

Influence of habitat on abundance and size structure of a large temperate-reef fish, Achoerodus viridis (Pisces: Labridae)

The relationship between densities of Achoerodus viridis (Pisces: Labridae) and reef habitats at various localities within New South Wales (NSW), Australia was examined. Types of habitats were quantified at inner, mid and outer estuarine locations in each of two estuaries (Botany Bay and Port Jackson) to determine whether purported patterns of movement from estuaries could be related to differences in habitat. Although the same types of habitat were generally found at all locations, differences in the proportion of habitat types were found between shallow and deep reefs and among inner, mid and outer estuarine locations for both estuaries. Shallow habitats were usually dominated by Ecklonia radiata, turf and/or fringe habitat in Botany Bay, whereas deep sites were generally dominated by urchin-grazed barrens habitat and, sometimes, sponge- and ascidian-dominated deep reef. Shallow sites in Port Jackson were dominated by a mixture of habitats, as were deep reefs at mid-estuarine locations. Other deep reefs in Port Jackson were dominated by E. radiata (inner estuarine) or barrens (outer estuarine) habitat. Thus, patterns of habitat cover were not consistent between estuaries and numbers of fish could not be related to proportional representation of habitat on reefs along estuarine gradients. Univariate and multivariate analyses showed that there was little evidence that any size class of fish was correlated with the proportional representation of a particular habitat or group of habitats. Counts of fish that focused on barrens and E. radiata forest habitats over a period of 10 yr showed that similar numbers and all sizes of fish were found in the two types of habitat. Greater numbers of small fish were, however, found in the E. radiata forest habitat than in the barrens habitat. Estimates of abundance along the coast of NSW (100s to 1000 km) in a range of habitats (e.g. ascidian-dominated reef, kelp forest, urchin-grazed barrens) showed that there was no indication that a particular habitat consistently had greater numbers of A. viridis than other habitats. Therefore, A. viridis of a range of sizes appears to be flexible in its use of habitats on reefs. Received: 24 December 1997 / Accepted: 23 June 1998     

Anthropogenic areas as incidental substitutes for original habitat

One speaks of ecological substitutes when an introduced species performs, to some extent, the ecosystem function of an extirpated native species. We suggest that a similar case exists for habitats. Species evolve within ecosystems, but habitats can be destroyed or modified by natural and human‐made causes. Sometimes habitat alteration forces animals to move to or remain in a suboptimal habitat type. In that case, the habitat is considered a refuge, and the species is called a refugee. Typically refugee species have lower population growth rates than in their original habitats. Human action may lead to the unintended generation of artificial or semiartificial habitat types that functionally resemble the essential features of the original habitat and thus allow a population growth rate of the same magnitude or higher than in the original habitat. We call such areas substitution habitats and define them as human‐made habitats within the focal species range that by chance are partial substitutes for the species’ original habitat. We call species occupying a substitution habitat adopted species. These are 2 new terms in conservation biology. Examples of substitution habitats are dams for European otters, wheat and rice fields for many steppeland and aquatic birds, and urban areas for storks, falcons, and swifts. Although substitution habitats can bring about increased resilience against the agents of global change, the conservation of original habitat types remains a conservation priority.     

土壤微生物呼吸热适应性与微生物群落及多样性对全球气候变化响应研究

土壤微生物呼吸热适应性被认为是决定陆地生态系统对全球变暖反馈作用的潜在重要机制,可能显著改变未来的气候变化趋势,然而,土壤微生物群落结构变化如何引起土壤微生物呼吸热适应性的研究目前尚存争议.该文针对气候变化对土壤微生物呼吸的影响研究,梳理了当前对土壤微生物呼吸的热适应性是否存在的争议和不同观点与结论,综述了气候变化对土...     

Species richness patterns along environmental gradients in island land molluscan fauna

The relationship between species richness and environmental variables may change depending on habitat structure, dispersal ability, species mixing, and community adaptation to the environment. It is crucial to know how these factors regulate the environment-diversity relationship. The land molluscan fauna of the Ogasawara Islands in the West Pacific is an excellent model system to address this question because of the high species endemicity (> 90%), small area, and simple habitat structure of the islands. I examined relationships among indigenous species composition, richness, and habitat condition, and especially productivity and forest moisture on the island of Anijima. Two major communities of snails could be distinguished by detrended correspondence analysis (DCA): one group dominated in a moist habitat with high productivity, and the other group dominated in a dry habitat with low productivity. However, species richness became highest at the intermediate condition between the habitats in which the two snail communities were dominant, so that species richness showed a hump-shaped relationship with moisture and productivity. In contrast, the species richness of the snail community in the moist habitat showed a monotonically positive correlation, and that in the dry habitat showed a monotonically negative correlation with moisture and productivity. Thus, the greater species richness in intermediate moisture and productivity resulted from the ecotone effect or community overlap at the transitional areas, where faunas with different ecologies can meet in a single site. These findings suggest that hump-shaped productivity-diversity relationships in land Mollusca would reflect the ecotone effect as a result of the mixing of species adapted to either fertile habitats or sterile habitats.     

Behaviour moderates climate warming vulnerability in high-rocky-shore snails: interactions of habitat use, energy consumption and environmental temperature

High-rocky-shore intertidal animals are predicted to be generally more vulnerable to climate warming than lower-shore species, because their thermal tolerances lie closer to maximum environmental temperatures (T _e). However, this prediction is based on taxonomically and ecologically limited information. The present study investigated the effect of habitat use on climate warming vulnerability of the tropical high-shore snail, Echinolittorina malaccana (from Brunei Darussalam, 5°N), which aestivates in sun-exposed or shaded habitats. The thermal regimes of these habitats differed vastly, but snails showed similar daily energy consumption in either habitat, due to temperature-insensitive metabolism (TIM) between 35 and 46 °C in the sun-resting snails. However, maximum T _e values in the shade and the sun were 35 and 46 °C, respectively, suggesting that sun-resting snails, which presently experience temperatures near the incipient lethal temperature range (46–56 °C), should be more threatened by further warming than shade-resting snails, which have an 11 °C ‘safety margin’. Thus, vulnerability of high-shore species to climate warming could be moderated by availability of shaded habitat, making predictions for these species more complex than previously realized.     

Habitat loss, trophic collapse, and the decline of ecosystem services

The provisioning of sustaining goods and services that we obtain from natural ecosystems is a strong economic justification for the conservation of biological diversity. Understanding the relationship between these goods and services and changes in the size, arrangement, and quality of natural habitats is a fundamental challenge of natural resource management. In this paper, we describe a new approach to assessing the implications of habitat loss for loss of ecosystem services by examining how the provision of different ecosystem services is dominated by species from different trophic levels. We then develop a mathematical model that illustrates how declines in habitat quality and quantity lead to sequential losses of trophic diversity. The model suggests that declines in the provisioning of services will initially be slow but will then accelerate as species from higher trophic levels are lost at faster rates. Comparison of these patterns with empirical examples of ecosystem collapse (and assembly) suggest similar patterns occur in natural systems impacted by anthropogenic change. In general, ecosystem goods and services provided by species in the upper trophic levels will be lost before those provided by species lower in the food chain. The decrease in terrestrial food chain length predicted by the model parallels that observed in the oceans following overexploitation. The large area requirements of higher trophic levels make them as susceptible to extinction as they are in marine systems where they are systematically exploited. Whereas the traditional species-area curve suggests that 50% of species are driven extinct by an order-of-magnitude decline in habitat abundance, this magnitude of loss may represent the loss of an entire trophic level and all the ecosystem services performed by the species on this trophic level.