Introduction

Conservation biology means different things to different people. For the purposes of this course, conservation biology covers all of those topics that I have chosen to include in the course and none of those topics that I haven't chosen to include. Seriously though, there are reasons I chose the topics I chose to include. To understand what they are, it may help to begin with a little history.

I don't think I have to convince anyone in this room that the world we now live in is far different from the one that was here a few thousand years ago. The reason for that difference is two-fold: the growth of human populations and the enormous resource demands we make on the planet.

• THE ENORMOUS INCREASE IN HUMAN POPULATION. The world had fewer than 3 billion people in in when I was born.¹ It reached 6 billion people in 1999. As of last Friday, it was nearly 7 billion  (http://www.census.gov/main/www/popclock.html; Figure 1), and the increase has been faster than exponential (Figure 2 (left)).²

  Figure 1: Estimates of the total human population of the United States and the world at 1:27pm EDT, 26 August 2011.

  

  Figure 2: Human population growth over the last million years (left) and projections through 2050 (right). Source: Roberts, L. 2011. 9 Billion? Science 333:540-543.

  

• That's the bad news. THE GOOD NEWS IS THAT RATES OF POPULATION GROWTH APPEAR TO HAVE SLOWED. The best guess from the United Nation's population program is that world population will reach a little over 9 billion by 2050 (Figure 2 (right)) and about 10 billion by the end of this century. That's 3 billion more than we have now,³. There's a lot of uncertainty about exactly how many people there will be at the end of the century. Fred Pearce [5] severely criticized the most recent U.N. projections, for example. Still, both the U.N. population council and its critics agree that there will be a little more than 9 billion people in the world by 2050, and that's a lot of people.

• THE ENORMOUS RESOURCE DEMANDS WE MAKE ON THE PLANET. Our numbers alone would be enough to ensure a great impact, but we also use many of the planet's resources. Peter Vitousek, Pam Matson, and Paul Ehrlich [8] estimated over 20 years ago that human beings capture over 40% of global net primary productivity, meaning that we are responsible for consuming nearly half of the annual energy input into the world's ecosystems. A more recent attempt to estimate the same quantity [6] emphasizes how little we now about our cumulative impact. Nonetheless, the authors estimate that humans appropriate at least 10% and possibly as much as 55% of terrestrial net photosynthetic production (TNPP). Their best estimate is that we appropriate about 32% of TNPP.

• But that's only the impact we have on net primary production. I can't do it, but it's conceivable that someone smarter than I am could imagine a scenario in which humans co-opt 50% of net primary production without a significant impact on other inhabitants of the earth. I can't come up with a sustainable scenario that allows us to co-opt 50% of net primary productivity because of how much we've already altered the face of the planet [9].
  • 10-15% of the earth's land surface is occupied by row-crop agriculture or by urban-industrial areas, and another 6-8% has been converted to pastureland. Total affected: between 15 and 25%, 40-50% of land surface has been transformed or degraded.

  • 22% of marine fisheries are overexploited or depleted, another 44% are at their limit of exploitation.

  • Humans use about 50% of the runoff water that is fresh and reasoably accessible. Human activities add at least as much fixed nitrogen to terrestrial ecosystems as all other sources combined.

  • Human activities are now responsible for fixing as much nitrogen as all terrestrial nitrogen fixation by bacteria, and anthropogenic nitrogen fixation is projected to increase by more than 60% between now and 2050 (Figure 3).

    Figure 3: Current and projected rates of annual nitrogen fixation due to human activities [1]

    

All in all, 83% of the earth's land surface has been directly influenced by human activities (Figure 4), and our impact is pervasive in densely populated areas like the northeastern United States (Figure 5). Peter Kareiva and colleagues point out that ``we have domesticated landscapes and ecosystems in ways that enhance our food supplies, reduce exposure to predators and natural dangers, and promote commerce'' [4, p. 1866]

Figure 4: The human footprint index reflects human population density, land transformation, access, and electrical power infrastructure [7]

Figure 5: The human footprint index clearly shows metropolitan areas in the northeastern United States. In addition to Boston and New York, which are labeled, it's easy to pick out Providence, RI, Hartford, CT, Springfield, MA, Worcester, MA, and Portland, ME. If you know the freeways in the area, it's not hard to pick out I-95, I-91, I-90, and others. (See http://sedac.ciesin.columbia.edu/wildareas/maps.jsp for more maps of the human footprint index.)

The Millenium Ecosystem Assessment [1] summarizes the four key findings of their study this way:

• Over the past 50 years, humans have changed ecosystems more rapidly and extensively than in any comparable period of time in human history, largely to meet rapidly growing demands for food, fresh water, timber, fiber, and fuel. This has resulted in a substantial and largely irreversible loss in the diversity of life on Earth.

• The changes that have been made to ecosystems have contributed to substantial net gains in human well-being and economic development, but these gains have been achieved at growing costs in the form of the degradation of many ecosystem services, increased risks of nonlinear changes, and the exacerbation of poverty for some groups of people. These problems, unless addressed, will substantially diminish the benefits that future generations obtain from ecosystems.

• The degradation of ecosystem services could grow significantly worse during the first half of this century and is a barrier to achieving the Millennium Development Goals.

• The challenge of reversing the degradation of ecosystems while meeting increasing demands for their services can be partially met under some scenarios that the MA has considered, but these involve significant changes in policies, institutions, and practices that are not currently under way. Many options exist to conserve or enhance specific ecosystem services in ways that reduce negative trade-offs or that provide positive synergies with other ecosystem services.

The changes have been so enormous that ten years ago Paul Crutzen proposed that we refer to the modern age as the Anthropocene [2], recognizing that humanity's impact on earth's systems will leave a geological imprint. The International Commission for Stratigraphy includes a Working Group on the Anthropocene within its Subcommission on Quaternary Stratigraphy. It's purpose is ``to examine the status, hierarchical level and definition of the Anthropocene as a potential new formal division of the Geological Time Scale'' (from the ``Outline of working group activities'' at http://www.quaternary.stratigraphy.org.uk/workinggroups/, accessed 26 August 2011). The Economist even put the Anthropocene on its cover last May (Figure 6) to accompany a leader⁴(http://www.economist.com/node/18741749) and a special feature (http://www.economist.com/node/18744401).

Figure 6: The cover of the 26 May edition of The Economist.