Vegetarianism and Wild Animals

Summary. It has been argued that promoting vegetarianism increases the number of animal life-years that exist because the reduced ecological footprint of the vegetarian diet allows many more animals to live in the wild. Since I think wild animals probably suffer more than they're happy, this may be a bad side-effect of vegetarianism. However, it may not be true that vegetarianism increases net wild-animal life-years. For example, even if crop farming reduces net animal populations without too much attendant suffering during the destruction process, climate change might increase long-term wildlife populations, and vegetarianism might offset this enough to switch the sign of the net impact. But in either case, I think the activities of organizations like Vegan Outreach and The Humane League are still overwhelmingly beneficial on balance because they encourage people to care more about animal welfare, which is important for reducing the likelihood that future humans vastly multiply wild-animal suffering.

Introduction

Animals raised in factory farms suffer enormously. Vegetarians aim to prevent this suffering by reducing the number of factory-farmed animals that exist. While many agree that this is a noble goal, the so-called Logic of the Larder claims that vegetarianism actually does a disservice to factory-farmed animals by denying them the chance to live.

Vegetarianism and Farm Land

Gaverick Matheny and Kai Chan respond to this charge in an excellent paper, Human Diets and Animal Welfare: The Illogic of the Larder. Suppose it were true -- contrary to the opinions of most observers -- that factory-farmed animals had lives worth living. Even in that case, those who want to create more happy animals should promote vegetarian diets because such diets allow more wild animals to exist. This is because less farm land is generally required to produce vegetable protein than factory-farmed animal protein, and the unused farm land supports greater abundance of wild-animal life than if it were cultivated. In particular, Matheny and Chan calculate that switching from a typical American omnivorous diet to a vegetarian diet causes a net increase of 0.6 animal life-years, counting both farmed and wild animals (pp. 586-587).

On pp. 587-588, Matheny and Chan note reasons that this figure may easily underestimate the increase in life-years that vegetarianism causes, perhaps by several orders of magnitude. One of the most important is that the authors counted life-years only for mammals and birds, since other taxa -- reptiles, amphibians, fish, and especially insects -- are less than certain to be sentient. This served to make their figures conservative, but a better utilitarian analysis for decision purposes would assign some probability to the sentience of these other organisms and include them accordingly. Doing so would, I think, cause wild-animal life-years to dominate the calculation. To see this, consider that the wild-animal densities Matheny and Chan used were on the order of 10³ per km² (p. 585), while arthropod densities are on the order of 10⁸ per acre, or 10¹⁰ to 10¹¹ per km².^[1] Even if we assigned an extremely low probability to arthropod sentience (say, 10^-3 or 10^-6), the expected densities would still be orders of magnitude higher than those for mammals and birds.

Does Crop Farming Increase or Decrease Insect Populations?

Matheny and Chan focus on agriculture's effect on wild mammal and bird populations and conclude that plant farming usually reduces these populations. What about for insects? Here, I'm uncertain on the sign of the net impact.

On the one hand, insecticides seem to decimate insects for short periods of time, possibly long enough that the prevented future births and deaths outweigh the acute pain caused by the insecticides themselves. On the other hand, agricultural crops are often very attractive to insects, and I would guess that many agricultural crops are designed to convert more sunlight into energy than wild plants, especially those growing in a forest where biomass creation is slower. More conversion of sunlight to energy means more total food, which means more insects can be supported -- if not on the crop lands themselves, then perhaps in other places where the food waste ends up.

This is speculation on my part. For example, maybe the herbicides used on crop fields actually keep plant populations fairly low relative to what would take their place? In any event, I think the issue deserves further study, but until then, it's not clear whether crop production actually decreases animal populations when we consider insects along with bigger animals.

Potential Relevance of Climate Change

In addition to freeing up farm land, vegetarianism has another major environmental impact: Reducing greenhouse-gas emissions. Eating a vegan diet instead of a conventional omnivorous American diet results in 1.485 fewer metric tons of CO2-equivalent gases per year. Assuming total emissions of 31.0 billion metric tons of CO2 by 2010 (see Figure 9 here), 1.485 metric tons represents a fraction 5 * 10^-11 of all human contributions to climate change in a given year.

On p. 587, Matheny and Chan acknowledge that their analysis omits externalities of agriculture like its contribution to global warming. However, the effect could be significant. To see this, suppose for illustration that global warming, say, increased the total animal population of the planet by 10%. Let's work just with mammal and bird populations to keep the figures comparable to those in the Illogic piece. A naïve estimate for the earth's total mammal-and-bird population based on Matheny and Chan's numbers would be something like (10³ individuals per km²) * (1.5 * 10⁸ km² of land on earth) = 1.5 * 10¹¹ individuals, so that a 10% increase represents 1.5 * 10¹⁰ individuals. Assuming that one year of greenhouse-gas emissions causes only one year of increased wild-animal populations and that the increase in animal populations due to global warming is a linear function of the amount of CO2-eq emitted, a vegetarian diet would -- by attenuating climate change -- reduce wild-animal life-years by (1.5 * 10¹⁰) * (5 * 10^-11) = 0.8, which is on the same order of magnitude as the changes due to agricultural land use, but in the opposite direction.^[2]

Will Climate Change Result in More or Fewer Wild Animals?

Of course, above I supposed that climate change would on the whole increase wild-animal populations, but this isn't completely obvious. Some of the consequences of global warming do suggest such a trend, including the following:

• Higher-latitude regions of the earth will become more tropical, and growing seasons will be longer.
• Increased CO2 concentrations reduce photorespiration, which translates into greater plant productivity (up to a point, until water or nutrients become limiting factors of growth).^[3]
• Several studies predict increases in insect populations due to climate change.^[4]

However, other consequences of climate change will reduce the number of animals living in the wild. For instance:

• Some currently tropical regions will turn to desert. Tropical regions will move north, but the speed of migration may be slow.^[5]
• Zooplankton biomass has been projected to decline 5-10% with doubling of CO₂.^[6] Reductions in zooplankton are relevant both insofar as zooplankton might be capable of suffering and because larger animals depend on zooplankton for food. Other research has tended to share the conclusion that climate change reduces copepod populations,^[7] although at least one has found the opposite.^[8]
• We might expect populations to decrease at least in the short term because animals have evolved to thrive in their current environments. It will take time for those species that don't go extinct to adapt to the changes.

There is no shortage of information on specific effects of climate change on various ecosystems, species, and biome patterns; e.g., Chapter 4 of the IPCC Fourth Assessment Report is a great place to start. On the other hand, it's easy to get bogged down in noisy point estimates and lose sight of the big-picture factors to consider. It may be that just one or two of the impacts of climate change dominates the others in the analysis -- what might those impacts be?

Assessing Climate-Change Impacts via Growth-Limiting Factors

One angle from which to study the likely effects of global warming on animal population sizes is to determine which are currently the limiting factors for growth in the major biomes of the world and then guess how climate change will affect those limiting factors (either by reducing the limitations or imposing new ones). For example:

• For insects in cooler climates (e.g., northern USA), one limiting factor is merely temperature: During the fall/winter, many insects die off and don't repopulate until spring/summer. If the temperature were warmer, they could survive all year. Food is not as much a limiting factor, because there are plenty of plants that aren't eaten even during the summer.
• For equatorial regions, is the limiting nutrient sometimes water? If so, this is why climate change will sometimes reduce animal populations through desertification.
• There are several growth-limiting factors for aquatic plants, including light, phosphorus, nitrogen, iron, etc. For animals, one limiting factor is dissolved oxygen, and warmer temperatures due to climate change will reduce dissolved oxygen availability, potentially reducing fish populations.

Lives Not Worth Living

For purposes of responding to the Logic of the Larder, Matheny and Chan grant the assumption that animal life-years have positive value. However, they note in a footnote on p. 586 that arguments have been made that neither set of animals [in factory farms nor in the wild] has lives worth living – their lives are filled with more misery than happiness (Ng, 1995). In this case, it would be best to adopt a diet that results in the fewest number of animal life-years.

I share Ng's concern that wild-animal lives may be on balance negative.

Promoting General Concern for Animals

I don't know the net directional impact of vegetarianism on suffering in the wild. I provisionally suspect that vegetarianism may prevent wild-animal suffering through reduced climate change, but I remain very uncertain and encourage others to improve the state of the research. That said, even if vegetarian diets did increase animal suffering by creating more wild animals, I don't think it's the case that organizations promoting vegetarianism do more harm than good. Exposure to the cruelties of factory farming is one way in which many people are first introduced to the topic of animal suffering in general, and I think that such concern can spill over into other domains, perhaps including suffering in nature. After all, if animals on factory farms would be better off not existing, then if conditions in the wild are for some animals just as miserable, then those animals would be better off not existing as well. And whether or not wild-animal lives are on the whole painful, it may be possible -- perhaps much farther off in the future -- to improve their welfare as is done for farm animals, such as by shifting from ecosystems filled with small, short-lived creatures that die young to ecosystems with larger, longer-lived animals.

General concern for animal suffering is crucial if humans are to make wise choices with respect to wild animals when they develop more advanced technologies, and utilitarian promotion of vegetarianism seems generally likely to cultivate such sympathies.^[9] Of course, raising awareness explicitly about animal cruelty in nature may be more effective -- and less potentially costly in its direct impact on suffering in the wild.

[1] One source mentions an estimate of 425 million arthropods per acre in forest. This paper cites estimates around 100-200 million per acre for crop land.

[2] I say only same order of magnitude because the 0.6 net life-years that vegetarianism creates when climate change is ignored counts farmed animals as well as wild animals.

[3] Figure 8 of this study reports increases in dry-matter production (DMP) generally between 0% and 30%. I would guess that more plant biomass usually implies more animal biomass because there's more food to be eaten, both by herbivores and decomposers. However, it's important to consider specific floral changes on a case-by-case basis; for instance, even though algae may grow faster with higher CO2 concentrations, they could also become less nutritious.

Also keep in mind that higher CO2 concentrations is an effect of emitting CO2 directly, rather than climate change generally, and a significant fraction of the global-warming contribution of meat comes from non-CO2 greenhouse gases like methane and nitrous oxides. Still, a vegetarian diet does produce less raw CO2 due to lower energy consumption, to the tune of about 0.7 metric tons per person per year (p. 10 here).

[4] From Erik E Stange and Matthew P Ayres, Climate Change Impacts: Insects:

• Warmer temperatures associated with climate changes will tend to influence (and frequently amplify) insect species’ population dynamics directly through effects on survival, generation time, fecundity and dispersal. [...]
• Insect populations in mid- to high latitudes are expected to benefit most from climate change through more rapid development and increased survival. Much less is known about the effects of increased warming on tropical insect species.
• Insect species’ mortality may decrease with warmer winter temperatures, thereby leading to poleward range expansions.

[5] From Biology by Robert J. Brooker, Eric P. Widmaier, Linda E. Graham, and Peter D. Stiling, pp. 1141-42:

Assuming this scenario of gradual global warming is accurate, we need to consider what the consequences might be for plant and animal life. At the beginning of the chapter, we saw how global warming is believed to be contributing to the decline and extinction of some amphibian species. Although many species can adapt to slight changes in their environment, the anticipated changes in global climate are expected to occur too rapidly to be compensated for by normal evolutionary processes such as natural selection. Plant species cannot simply disperse and move north or south into the newly created climatic regions that will be suitable for them. Many tree species take hundreds, even thousands, of years for seed dispersal. Paleobotanist Margaret Davis predicted that in the event of a CO₂ doubling, the sugar maple (Acer saccharum), which is presently distributed throughout the Midwestern and northeastern U.S. and southeastern Canada, would die back in all areas except in northern Maine, northern New Brunswick, and southern Quebec. Of course, this contraction in the tree’s distribution could be offset by the creation of new favorable habitats in central Quebec. However, most scientists believe that the climatic zones would shift toward the poles faster than trees could migrate via seed dispersal; therefore, extinctions would occur.

[6] From Anthony J. Richardson, In hot water: zooplankton and climate change:

Dynamics of plankton communities at a first approximation are captured by nutrient–phytoplankton–zooplankton (NPZ) models. [...] NPZ models can be coupled to [general circulation models] GCMs of the Earth's climate system, allowing investigation of the potential future states of plankton communities under alternative projections of climate.

Results from the NPZ model of Bopp et al. (2004, 2005) suggest that under doubling of pre-industrial CO₂ levels, global primary productivity may decline by 5–10%. This trend is not uniform, but indicates productivity increases of 20–30% in high latitudes and marked declines in the stratified tropical oceans (Figure 10). This and other models generally suggest that warmer, more stratified conditions in the tropics will reduce nutrient concentrations in surface waters, which will lead to smaller phytoplankton cells dominating over larger diatoms, thereby lowering zooplankton biomass. [...]

There is already observational evidence supporting some of these model projections. Decreased nitrate availability was apparent in the 20th century during warm periods in both hemispheres, and a decreasing trend is clearly evident globally since the 1970s (Kamykowski and Zentara, 2005). Ocean colour satellite data based on CZCS (1979–1986) and SeaWiFS (1997–2000) show that global ocean phytoplankton chlorophyll decreased 8% from the early 1980s to the late 1990s (Gregg and Conkright, 2002). Behrenfeld et al. (2006) demonstrate that global, depth-integrated chlorophyll biomass since 1999 has dropped by an average of 0.01 Tg year−1. This decline was driven by El Niño-like climatic conditions that enhanced stratification in the expansive stratified low-latitude oceans and consequently reduced nutrient availability for phytoplankton. As some climate models predict more permanent El Niño conditions in a warmer system state, this study suggests that the abundance and productivity of plankton communities in the tropical oceans could decline in the future. There is also some evidence that global time-series of zooplankton abundance are declining in the tropical North Atlantic (Piontkovski and Castellani, 2007). Any future reductions in primary and secondary productivity and export production will not only reduce the food available for higher trophic levels in pelagic ecosystems, but will also impact deep ocean communities (Ruhl and Smith, 2004).

[7] From Zooplankton and Climate Change – the Calanus Story:

The planktonic copepod Calanus finmarchicus is an important component of the North Sea food web, channelling energy from primary production to harvestable fish resources, and is therefore an indicator of the state of the marine food web. During the 1960s the biomass of Calanus in summer constituted up to 70% of all zooplankton in the northern North Sea, but since then its abundance has declined, so that in the late 1990s its biomass is only around 50% of that found 30 years earlier.

There is a strong statistical relationship between the abundance of Calanus finmarchicus in the northern North Sea and an atmospheric index of climate in the North Atlantic – the North Atlantic Oscillation (NAO) index. Research at Fisheries Research Services (FRS) has identified the likely oceanographic basis for this relationship as a combination of changing wind patterns in spring, and a steady decline in the volume of cold bottom water in the Faroe-Shetland Channel. In the winter, at depths greater than 600 m, the bottom water contains large numbers (up to 650 m^-3) of hibernating Calanus finmarchicus. In the spring these copepods ascend to the surface waters again, and many are carried into the North Sea, maintaining the productive summer stock. The FRS studies indicate that the changes in wind patterns and declining volume of bottom water have effectively reduced the supply of copepods to the North Sea.

From Joseph Kane and Jerome Prezioso, Distribution and multi-annual abundance trends of the copepod Temora longicornis in the US Northeast Shelf Ecosystem:

Temora longicornis abundance in the ecosystem's southernmost subarea (Middle Atlantic Bight) did not increase in the 1990s and was found to be negatively correlated to surface temperature, indicating that continued global warming could adversely impact the copepods annual abundance cycle in this region. [...]

The effects of continued global warming would most likely have the greatest impact on the seasonal abundance cycle of T. longicornis in the southernmost [Middle Atlantic Bright] MAB region. Mean abundance there declines sharply as temperature rises in summer (Fig. 13) and annual levels are lower during warmer years. This negative relationship with temperature is likely caused by a combination of two factors: (i) reduced food concentrations after the spring bloom (Maps et al., 2005; Hansen et al., 2006) and (ii) the deleterious effect of rising temperatures on egg production rates (Peterson and Kimmerer, 1994; Halsband and Hirche, 2001). Long-term data indicates that the range of sea surface temperature on the US northeast shelf is increasing, producing faster warming and cooling rates during seasonal transitions (Friedland and Hare, 2007). Continued warming will likely impact T. longicornis by altering the timing of the spring bloom and raising daily metabolic requirements, lowering rations available for growth and reproduction. Since studies have shown that shelf waters in the region have warmed during the 1990s, with significantly warmer values found during winter (Mountain, 2004; Sullivan et al., 2005), it may not be long before the peak abundance period of T. longicornis is shortened and minimized in the MAB.

One slide in a presentation by Carmen García-Comas, Climate change and copepod size spectra: Comparison of two coastal long-term series in the western Mediterranean Sea, notes this trend: Higher water temperature: Lower primary production.

[8] Climate change study warns against one-off experiments:

Dr Mayor said: "Both of our experiments indicated that the health of copepod eggs remains unaffected when they are exposed to ocean acidification levels predicted for the end of the 21st century. This is great news.

"However our previous research has demonstrated that more severe acidification, potentially arising if a subsea carbon capture reservoir burst open, causes a major decline in the number of copepod eggs that successfully hatch.

"Our most recent study found that the effect of global warming depends on when the eggs were collected.

"In our first experiment we found no clear effect of temperature on how many hatchlings were produced by the eggs.

"But in the second experiment, conducted a week later, increasing the seawater temperature actually increased the number of healthy hatchlings."

Researchers believe this effect relates to the temperature at which the maternal copepods were acclimated - animals from warmer waters produce eggs that are less stressed by warm water and vice versa.

Dr Mayor added: Our results highlight a potentially positive effect of global warming - it may increase the number of healthy copepods in our seas, which is good news [sic] for the larvae of fish such as cod and herring, and ultimately fishermen. [sigh :(]

[9] On the other hand, promoting vegetarianism from, say, the perspective that humans have no right to interfere with animals could be counterproductive.

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