CHAPTER 38 Conservation Biology Modules 38.6 – 38.8

38.6 There are two approaches to studying endangered populations CONSERVATION OF POPULATIONS AND SPECIES 38.6 There are two approaches to studying endangered populations Habitat degradation can lead to population fragmentation Portions of populations are split and subsequently isolated It often results in species being designated as threatened or endangered Figure 38.6A

The Endangered Species Act (ESA) defines an endangered species as one that is in danger of extinction throughout all or a significant portion of its range Example: the northern spotted owl The ESA defines a threatened species as one that is likely to become endangered in the foreseeable future Figure 38.6B

The small-population approach Some conservation biologists believe that the smallness of a population will ultimately drive it to extinction The small-population approach Identifies the minimum viable population size for a threatened species Focuses on preserving genetic variation The declining-population approach diagnoses and treats the causes of a population's decline

The red-cockaded woodpecker requires three habitat factors 38.7 Identifying critical habitat factors is a central goal in conservation research Identifying the specific combination of habitat factors that is critical for a species is pivotal in conservation biology The red-cockaded woodpecker requires three habitat factors A mature pine forest Figure 38.7A

Low growth of plants among the mature pine trees Controlled fires to reduce forest undergrowth Figure 38.7B, C

Increased fragmentation threatens many species 38.8 Connection: Increased fragmentation threatens many populations: A case study Increased fragmentation threatens many species This includes those whose populations were historically highly fragmented

One example is the endangered bull trout It inhabits lakes, rivers, and mountain streams in northwestern Canada and the United States Figure 38.8A

The bull trout requires cold, fast-flowing streams with pebble-covered bottoms and little or no silt Figure 38.8B

Before human intervention, the bull trout population consisted of four subpopulations Egg-laying sites in mountain streams Regular, frequent dispersal and gene flow between subpopulations Irregular, infrequent dispersal; minimal gene flow between subpopulations Figure 38.8C, left

The bull trout population has been further fragmented and reduced by Mill site for silver mine the construction of hydroelectric dams logging road building mining s3 s5 s4 Hydroelectric dam Hydroelectric dam Egg-laying sites in mountain streams Clear-cut (logged) areas Roads Irregular, infrequent dispersal; minimal gene flow between subpopulations Figure 38.8C, right

Conservation biologists often use computer simulations in a population viability analysis (PVA) PVA incorporates as much information about a population's current status as available It predicts a species' chance for long-term survival