Chapter 58

1. Biodiversity loss is the loss of diversity at genetic, population, species, ecosystem, and global scales. The four major causes of biodiversity loss are habitat destruction (reduction in habitat quantity) and degradation (reduction in habitat quality); overharvesting of species; species invasions and emerging diseases; and climate change.

2. The heath hen’s population sizes were reduced by hunting until only one very small population remained on the island of Martha’s Vineyard, Massachusetts, in 1830. By 1908 only 50 birds remained. Although the population recovered to several thousand birds once a reserve was established for them, human-caused and natural factors led to a precipitous decline. The reduction in size caused inbreeding depression and demographic stochasticity and reduced the effective population size even more. By 1928 there were 2 females and 11 males, not enough individuals or genetic diversity to save the heath hen from extinction.

3. There are multiple reasons why it is hard to determine how many species are extinct or threatened with extinction. First, we do not know how many species live on Earth today because many have not been described. Some of those undescribed species may have already become extinct. Second, many described species are small, reclusive, and rare, and thus hard to keep track of. Third, it is difficult to determine whether a species is truly extinct, especially if it is rare. For example, there have been cases in which species were thought to be extinct but were later discovered to still be extant. Fourth, we rarely know all the interactions among species. It is hard to determine if the loss of one species will lead to the loss of others unless we have detailed ecological knowledge of all the species affected.

1. The more fragmented a habitat is, the smaller and more isolated the fragments are and the greater the edge effects are. Fragmentation reduces the population sizes of species and isolates them from one another, reducing their ability to disperse among the greater metapopulation. Once population sizes are small and isolated, they become susceptible to extinction vortex processes (see Figure 58.2).

2. Gray wolves have been shown to create a trophic cascade that benefits hardwood trees such as aspens. Research by William Ripple and colleagues in Yellowstone National Park found that gray wolves, by feeding on elk, released aspen seedlings from herbivory, thus creating mature aspen forests. After wolves were hunted to extinction in Yellowstone in 1926, the number of aspens declined precipitously because of intensive elk grazing, as is shown in Figure 56.9.

3. A-62

   Three reasons why invasive species can have negative effects on biodiversity and ecosystems are (1) they can threaten native species with extinction through predation, competition, and disease transmission; (2) they can change the functions and services of ecosystems by affecting fire cycles, water availability, and sedimentation; and (3) they can change the genetic diversity of native species through hybridization events.

4. Yes, these data strongly suggest that climate warming is causing the butterfly species to shift its distribution to cooler, more optimal temperature conditions farther north. Likewise, emergence time is occurring earlier, when temperature conditions are optimal for that stage of the species’ life history.

1. Reserve design relies on three important principles: first, identify a large enough area that is relatively undisturbed and can serve as the core for protection; second, include a buffer zone around the core area that has some features required by the species of concern but is less restrictive to human use; and third, have habitat connectivity that keeps populations from becoming isolated from the greater metapopulation and thus subject to extinction. Taking into account global warming in terrestrial systems, the protected area should have similar protected areas, potentially connected by corridors of land, to the north (or south in the southern hemisphere) that could serve as a refuge from warming temperatures. An example is the Yellowstone to Yukon Conservation Initiative discussed in the chapter.

2. The California condor declined in its native range (British Columbia to Mexico) because of lead poisoning from carcasses containing lead shot, electrocution from power lines, the effects of pesticides on eggshell thinning, and hunting (ecological information). To save the California condor from extinction, the Endangered Species Act (institutional authority) was invoked and the species was removed from the wild in 1983 and subsequently bred in captivity. Although the breeding program was successful, ecological information indicated that birds could not be released into the wild until the threats that caused their decline were mitigated. In 2008, the Ridley–Tree Condor Preservation Act was passed to require California hunters to use non-lead bullets when hunting in the condor’s range. Along with passage of the act, public awareness was raised for hunters and cattle ranchers who mistakenly believed that condors killed livestock (socioeconomic interests).

1. Distance interval (km)	Time interval (years)	Rate of spread (km/yr)
   0–140 = 140	1987–1993 = 6	140/6 = 23
   140–240 = 100	1993–1996 = 3	100/3 = 33
   240–325 = 85	1996–2002 = 6	85/6 = 14
   325–410 = 85	2002–2004 = 2	85/2 = 43
   410–445 = 35	2004–2006 = 2	35/2 = 18

   The rates of spread do differ. They range from 14 to 43 km/year depending on the location.

2. The average rate of Bd spread is 26 km/year. Assuming this average, the pathogen could spread 260 km east and south by 2016 (26 km/yr × 10 years).

3. The majority of the habitat east and south of the last location where Bd was detected is mostly low elevation (0–199meters), although there is a thin stretch of mountain habitat in the north. Given that far fewer frog species have become extinct because of Bd at elevations of 199 meters or less (30%), it seems less likely that the pathogen will be successful in this region of Panama. Based on the elevation data, the species extinction might reach 30%.

1. Vehicle collisions and hunting, both legal and illegal, are the two known major causes of puma deaths in these populations. Suspected and confirmed diseases together rank as the third most common cause. The two major causes result from human actions, particularly loss of habitat and/or habitat degradation, which forces pumas into urban and suburban areas. Disease is presumably a natural cause.

2. As effective population size decreases, a population enters an “extinction vortex,” decreasing more every year and becoming more likely to go extinct. The pumas are living in an increasingly urban area and are at risk from vehicle collisions, hunting (both legal and illegal), and other urban-based factors, in addition to natural risks. As their population size declines, their genetic diversity also declines, making successful reproduction less likely. These factors suggest that, without some kind of intervention, pumas in these two populations will soon go extinct (with the Santa Ana population dying out first).

3. Maintaining any population and saving it from loss or extinction contributes to biodiversity, because all species and populations are part of biodiversity. Each lost population represents the loss of a strand in the web of life, which is connected to other strands (species) in the community. The puma, as a top predator, contributes to control of its prey populations, which in turn affects lower levels in the food chain, down to producers. Loss of the puma could therefore affect community structure at several levels. This in turn will limit the effectiveness of ecosystem functions and the ecological services (both practical and aesthetic) provided by California ecosystems.

4. Both populations are very small, so it makes sense to maximize the size of the gene pool by attempting to conserve both populations. However, finding an appropriate protected area might skew the protection toward one population: the less urbanized Peninsular Range population. If a protected area is identified in the Peninsular Range, habitat corridors could be provided to connect this population with the Santa Ana population, thus extending protection to both populations.

5. In a coupled human−natural system, humans in urban and suburban areas are enlisted to increase biodiversity in their own habitats. For small species (such as pollinators), people can plant native gardens or even window boxes. This is more difficult, but still possible, for large top predators, such as pumas, with large geographic ranges. If conservationists establish a protected area for pumas in the Peninsular Range, a fairly large buffer zone would need to be established around it. The buffer zone would involve agricultural areas, and farmers would need to help maintain it. This would involve an extensive education program, since many farmers see pumas as “the enemy.” (In fact, the legal hunting that causes many puma deaths results from pumas feeding on livestock after being forced out of their natural habitat.) Farmers could be encouraged to establish edge habitats on their properties, allowing pumas safe passage to wilder areas. Coupled human−natural systems friendly to pumas would be more difficult to establish in urban areas, but wildlife corridors—particularly those allowing safe passage across highways—would be one obvious example.