Paul R. Ehrlich

Human Appropriation of the Products of Photosynthesis

Earths resources are consumed by one of its 5-30 million species homo sapiens or man at a rate disproportionately greater than any other species. Mans impact on the biosphere is measured in terms of net primary production (NPP). NPP is the amount of energy remaining after the respiration of primary producers (mostly plants) is subtracted from the total amount of biologically fixed energy (mostly solar). Human output is determined by 1) the direct NPP used for food fuel fiber or timber which yields a low estimate 2) all NPP of cropland devoted to human activity and 3) both 1) and 2) and land conversion for cities or pastures as well as conversion which results in desertification and overuse of lands. This last output determination yields a high estimate. Calculations are made for global NPP and each of the 3 estimates of low intermediate and high human output. Data are based on estimates by Ajtay et al. Armentano and Loucks and Houghton et al. and on the Food and Agriculture Organizations (FAO) summaries. Petagram (Pg) is used to calculate organic matter; this is equivalent to 10 to the 15th power grams or 10 to the 9th power metric tons. Carbon has been converted to organic matter by multiplying by 2.2. Matter in kilocalories has been converted to organic matter by dividing by 5. Intermediate or conservative estimates have been included. The standard of biomass is 1244 Pg and an annual NPP to 132.1. The NPP of marine and freshwater ecosystems is considered to be 92.4 Pg which is a low estimate. The low calculation of human (5 billion persons) consumption of plants at a caloric intake of 2500 kilocalories/person/day is .91 Pg of organic matter which equals .76 Pg of vegetable matter. The global production of human food is 1/7 Pg for grains and for human and livestock fed or .85 Pg of dry grain material and .3 Pg in nongrain dry material with dry grain material and .3 Pg in nongrain dry material with a subtraction of 20% for water content. 34% or .39 Pg is lost to waste and spoilage. Consumption by livestock forest usage and aquatic ecosystems is computed. The overall estimate for human use if 7.2 Pg of organic matter/year or 3% of total NPP/year. The intermediate figures take into account cropland pastureland forest use and conversion; the overall estimate of human use is 42.6 Pg of NPP/year of 19.0% (42.6/224.5) of NPP (30.7% on land and 2.2% on seas). The high estimate yields human use of 58.1 Pg/year on land or 40% (58.1/149.6) of potential land productivity or 25% (60.1/149.8 + 92.4) of land and water NPP. The remaining 60% of land is also affected by humans. The figures reflect the current patterns of exploitation distribution and consumption of a much larger population. These patterns amount to using >50% of NPP of land; there must be limits to growth.

Human appropriation of renewable fresh water

Humanity now uses 26 percent of total terrestrial evapotranspiration and 54 percent of runoff that is geographically and temporally accessible. Increased use of evapotranspiration will confer minimal benefits globally because most land suitable for rain-fed agriculture is already in production. New dam construction could increase accessible runoff by about 10 percent over the next 30 years, whereas population is projected to increase by more than 45 percent during that period.

Are We Consuming Too Much

This paper articulates and applies frameworks for examining whether consumption is excessive. We consider two criteria for the possible excessiveness (or insufficiency) of current consumption. One is an intertemporal utility-maximization criterion: actual current consumption is deemed excessive if it is higher than the level of current consumption on the consumption path that maximizes the present discounted value of utility. The other is a sustainability criterion, which requires that current consumption be consistent with non-declining living standards over time. We extend previous theoretical approaches by offering a formula for the sustainability criterion that accounts for population growth and technological change. In applying this formula, we find that some poor regions of the world are failing to meet the sustainability criterion: in these regions, genuine wealth per capita is falling as investments in human and manufactured capital are not sufficient to offset the depletion of natural capital.

Biodiversity Studies: Science and Policy

Biodiversity studies comprise the systematic examination of the full array of different kinds of organisms together with the technology by which the diversity can be maintained and used for the benefit of humanity. Current basic research at the species level focuses on the process of species formation, the standing levels of species numbers in various higher taxonomic categories, and the phenomena of hyperdiversity and extinction proneness. The major practical concern is the massive extinction rate now caused by human activity, which threatens losses in the esthetic quality of the world, in economic opportunity, and in vital ecosystem services.

Accelerated modern human–induced species losses: Entering the sixth mass extinction

Humans are causing a massive animal extinction without precedent in 65 million years. The oft-repeated claim that Earth’s biota is entering a sixth “mass extinction” depends on clearly demonstrating that current extinction rates are far above the “background” rates prevailing between the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, we use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. We then compare this rate with the current rate of mammal and vertebrate extinctions. The latter is conservatively low because listing a species as extinct requires meeting stringent criteria. Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 100 times higher than the background rate. Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing.

Ecosystem consequences of bird declines

We present a general framework for characterizing the ecological and societal consequences of biodiversity loss and applying it to the global avifauna. To investigate the potential ecological consequences of avian declines, we developed comprehensive databases of the status and functional roles of birds and a stochastic model for forecasting change. Overall, 21% of bird species are currently extinction-prone and 6.5% are functionally extinct, contributing negligibly to ecosystem processes. We show that a quarter or more of frugivorous and omnivorous species and one-third or more of herbivorous, piscivorous, and scavenger species are extinction-prone. Furthermore, our projections indicate that by 2100, 6–14% of all bird species will be extinct, and 7–25% (28–56% on oceanic islands) will be functionally extinct. Important ecosystem processes, particularly decomposition, pollination, and seed dispersal, will likely decline as a result.

Effects of household dynamics on resource consumption and biodiversity.

Human population size and growth rate are often considered important drivers of biodiversity loss, whereas household dynamics are usually neglected. Aggregate demographic statistics may mask substantial changes in the size and number of households, and their effects on biodiversity. Household dynamics influence per capita consumption and thus biodiversity through, for example, consumption of wood for fuel, habitat alteration for home building and associated activities, and greenhouse gas emissions. Here we report that growth in household numbers globally, and particularly in countries with biodiversity hotspots (areas rich in endemic species and threatened by human activities), was more rapid than aggregate population growth between 1985 and 2000. Even when population size declined, the number of households increased substantially. Had the average household size (that is, the number of occupants) remained static, there would have been 155 million fewer households in hotspot countries in 2000. Reduction in average household size alone will add a projected 233 million additional households to hotspot countries during the period 2000–15. Rapid increase in household numbers, often manifested as urban sprawl, and resultant higher per capita resource consumption in smaller households pose serious challenges to biodiversity conservation.

Should agricultural policies encourage land sparing or wildlife‐friendly farming?

As the demands on agricultural lands to produce food, fuel, and fiber continue to expand, effective strategies are urgently needed to balance biodiversity conservation and agricultural production. “Land sparing” and “wildlife-friendly farming” have been proposed as seemingly opposing strategies to achieve this balance. In land sparing, homogeneous areas of farmland are managed to maximize yields, while separate reserves target biodiversity conservation. Wildlife-friendly farming, in contrast, integrates conservation and production within more heterogeneous landscapes. Different scientific traditions underpin the two approaches. Land sparing is associated with an island model of modified landscapes, where islands of nature are seen as separate from human activities. This simple dichotomy makes land sparing easily compatible with optimization methods that attempt to allocate land uses in the most efficient way. In contrast, wildlife-friendly farming emphasizes heterogeneity, resilience, and ecological inter...

Population diversity and ecosystem services

Abstract The current rate of biodiversity loss threatens to disrupt greatly the functioning of ecosystems, with potentially significant consequences for humanity. The magnitude of the loss is generally measured with the use of species extinction rates, an approach that understates the severity of the problem and masks some of its most important consequences. Here, we propose a major expansion of this focus to include population diversity: considering changes in the size, number, distribution and genetic composition of populations and the implications of those changes for the functioning of ecosystems and the provision of ecosystem services. We also outline the key components of population diversity and describe a new approach to delineating a population unit that explicitly links it to the services that it provides

Disappearance of insectivorous birds from tropical forest fragments

Determining the impact of forest disturbance and fragmentation on tropical biotas is a central goal of conservation biology. Among tropical forest birds, understory insectivores are particularly sensitive to habitat disturbance and fragmentation, despite their relatively small sizes and freedom from hunting pressure. Why these birds are especially vulnerable to fragmentation is not known. Our data indicate that the best determinant of the persistence of understory insectivorous birds in small fragments is the ability to disperse through deforested countryside habitats. This finding contradicts our initial hypothesis that the decline of insectivorous birds in forest fragments is caused by impoverished invertebrate prey base in fragments. Although we observed significantly fewer insectivorous birds in smaller fragments, extensive sampling of invertebrate communities (106,082 individuals) and avian diets (of 735 birds) revealed no important differences between large and small fragments. Neither habitat specificity nor drier fragment microclimates seemed critical. Bird species that were less affected by forest fragmentation were, in general, those that used the deforested countryside more, and we suggest that the key to their conservation will be found there.