Conservation Approaches: Species, Landscapes, and Demography

Most conservation efforts have focused on protecting individual species or populations of single species. Why?

1. Species and populations are the essential unit of evolution

2. Legal mandates are typically centered at the species level (e.g., U.S. Endangered Species Act; Convention on International Trade in Endangered Species = CITES)

3. Education: efforts to engage the public on conservation issues are often tied to the public’s interest in certain high-profile species (e.g., giant panda, gray wolf, sea turtles)

4. Ecological theory on which conservation is based has traditionally focused on species

5. Passion! Conservationists, including conservation biologists, develop a deep, personal and professional interest in a particular species; this duty of care fosters an interest in saving them from extinction

Criticism of ecosystem-level protection

• protected areas are often not properly enforced (e.g., Dulvy, 2013)

• To be clear, we need both strategies to win battles for biodiversity

• There are also individual conservationists that have made tremendous contributions towards saving single species (e.g., Jane Goodall, Dian Fossey)

How do we decide a species needs conserving?

• population declining

BIDE Factors

birth rates (B), immigration (I), death rates (D), & emigration (E)

So Nt+1 = Nt + B + I – D – E, where N = population size at time t

there are also secondary demographic factors called life history characteristics

such as sex ratio, age structure, timing of first reproduction/age at maturity, size at maturity

importance of demography in in conservation biology - ex Key Deer

• a race of White-tailed Deer that live in the Florida keys

• They are found on 20 islands, with 75% found on two islands: Big Pine Key and No Name Key

• Although they mainly live on a National Wildlife Refuge, mortality occurs due to habitat loss, vehicle collisions & ‘deaths associated with urbanization’

• Lopez et al (2003) showed that vehicle collisions caused > 50% of all adult deaths. In the meantime managers were taking conservation measures to reduce collisions such as fencing, underpasses & cattle guards

• However, Lopez et al (2003) also determined that the populations were near carrying capacity, and so reducing mortality due to collisions might increase populations and thus the spread of disease, and increase negative human-deer interactions

• Although all agreed that reducing collisions is desirable, they also suggested actions be taken to reduce birth rates (e.g., contraception) to compensate for the decrease in mortality due to measures to reduce collisions

• Conservation of these populations benefitted from understanding and manipulating demography

How are populations (mainly) regulated

• Increased mortality or decreased natality due to shortage of resources (e.g., shortage of food)

• Increased mortality or decreased natality due to increased intensity of intraspecific interactions (i.e., competition)

• Increased mortality due to increased predation, parasitism or disease

Density dependence

c - birth rates

b - death rates

a - density independence

problems of small populations

• allee effect

• inbreeding depression

• demographic uncertainty/stochasticity

• environmental uncertainty/stochasticity

allee effects

at a very low population density there can be problems relating to social behavior

inbreeding depression

loss of genetic diversity (alleles) due to small sample size associated with breeding among close relatives

demographic uncertainty/stochasticity

attributes such as mortality rate and reproductive success - can be highly variable among individuals, such that if the population is too small the population can go extinct

environmental uncertainty/stochasticity

sudden unpredictable increase in mortality or reproductive failure (e.g., due to floods, storms, droughts, etc)

source population

that good habitats result in higher survival and reproductive success

Populations produce an excess of individuals that must disperse outside their habitats

sink population

poor habitats result in lower survival and reproductive success (rely on source)

populations in would become extinct without dispersing individuals from source populations

metapopulations

A population that consists of many subpopulations linked by dispersal

source populations are defined by

demography (survival and reproductive success), not population density

Metapopulations - ex: Peregrine Falcon conservation

• Populations crashed starting in the 1950’s due to the pesticide DDT

• After DDT was removed from use, northern California (CA) populations began to recover while coastal CA populations did not

• A third population type – in urban areas – rebounded quickly because of high survival in young birds due to lack of predators & easy prey = pigeons (Kaufmann et al., 2004)

• Source-sink modeling showed that northern populations would persist without intervention, & could theoretically serve as a source population for the coastal populations

• However, northern birds rarely dispersed, and so the coastal populations would possibly go extinct without the addition of hundreds of captive-bred young; this was carried out successfully

what do you need to know to determine which habitats/populations are sources vs sinks

a great deal of knowledge about the demography & natural history of organisms. Without this knowledge, it is impossible to design and implement an effective conservation plan

the cougar story

• Extirpated in the eastern and central U.S. in the early 1900’s (except in south Florida)

• Almost hunted to extinction in the western U.S.

• In the 1980’s ‘green movements’ in states such as Colorado encouraged their protection around suburban park areas

• Human-cougar interactions increased dramatically

• Sightings indicate that they are moving eastward

Wildlife – human interactions

• Black Bears have killed 61 people in North America since 1900

• Grizzly Bears have killed 8 people at Yellowstone NP in 140 years

• Spiders kill 7 people annually in NA

• Snakes kill 5 people annually in NA

• Domestic dogs kill 35 people annually in NA

• Lightning kills 31 people annually in the U.S.

• Car accidents kill ~37,000 people annually in the U.S.

• Guns kill ~34,000 people annually in the U.S.

Modeling approaches in conservation

▪Conservation biologists often rely on quantitative models to predict the fate of populations, and to test scenarios that may explain decline or indicate what kinds of interventions are more likely to succeed

population viability analysis (PVA)

Examines the demographic effect of different threats or management practices on a population(s) by projecting into the future. Basically we are trying to understand extinction risk

• Data plugged into the model include life span, age-specific growth rate, age-specific mortality rates & fecundity

• There have been numerous criticisms based on data limitations & uncertainties, and the lack of testing predictions in the short term

Population change and hierarchical analysis

• Predicting and understanding population change can be complex, and can be best viewed in a hierarchy comprised of 3 levels:

  • Landscape level, population level, individual level

• Population dynamics should thus be as a hierarchy of processes affecting populations at different levels

  

Landscape models for conservation

• Source-sink dynamics require conservationists and land managers to adopt a landscape approach; the fates of populations linked by dispersal are interconnected

• The landscape approach to conservation recognizes the interconnectedness of populations and incorporates this into models and management plans

• For example, saving a single piece of critical habitat may not be enough to maintain a population

How is the landscape perspective developed and applied in the field?

A conservation biologist or ecologist is interested in mapping the landscape at the appropriate scale - sensitive enough to capture the habitat requirements but large enough to cover the area an organism will occupy during its lifetime

Mapping boundaries of habitat patches requires a set of criteria that is easiest in disturbed landscapes, harder in natural landscapes, and often not possible in marine landscapes

landscape

is a mosaic of patches of habitat across which organisms move, settle, forage, reproduce, and die

Bachman’s Sparrow habitat mapping

• Soil type & topography influence the rate at which seedling trees grow, and thus the ages of pine stands that have vegetation profiles suitable for the sparrows

  • These can also be mapped for managers

• The habitat requirements will obviously differ among species

• The maps will not always determine the presence or absence of a species, but it can categorize habitats as suitable or non-suitable, or even provide a probability of occupation

Landscape models informing conservation

Liu et al. (2001) studied changes in habitat for Giant Pandas in China

China, along with WWF, set aside a series of reserves for panda protection in mountainous areas; only a fraction of each reserve contained suitable habitat for bamboo (the panda’s food)

Ecotourism of the reserves benefitted local people in the rural areas; this caused the rate of habitat destruction of panda habitat inside the reserves to increase since reserve establishment

Locals had cleared land for firewood and materials for the increasing human population; landscape modeling demonstrated the loss of habitat

landscape mapping - biosphere reserves

spatially-explicit population models (SEPM)

• incorporate the actual locations of organisms and suitable patches of habitat, and explicitly consider the movement of organisms among those patches

  • They are composed of 3 elements: a landscape map, a scenario of how the landscape will change in the future, & a population dynamics simulation

• Metapopulation models are general and do not incorporate the complexities of real landscapes; they are thus of limited use for conservation managers

Mobile Animal Population (MAP)

• type of SEPM that simulates habitat-specific demography and the dispersal behavior of organisms on computer representations of real landscapes

• The map is a grid of cells, each of which is the size of an individual territory of the species being simulated; models contain information on management practices, succession, and growth rates of important other species (e.g., trees)

• The model can depict the current landscape structure and project the landscape structure in the future based on a management plan specifying a harvest and replanting schedule

Geographical information Systems (GIS)

• a system designed to capture, store, manipulate, and analyze all types of geographical data - roads, patches of habitat, trees, farms, rivers, etc

• incorporate and maps the actual distribution of habitat patches in a region using satellite

Alternative Future analysis

predicts outcomes in both biodiversity and socioeconomics based on several projections of future development

example of landscape-based demographic model

• > 50% of birds that breed in North America are Neotropical migrants – that is, they overwinter in Central and South America

• Many are in decline due to habitat loss & fragmentation

• SEPM modeling was used to assess the extinction risk of these birds in the face of landscape change; or, how species might respond to various land management scenarios