BCB 341: Principles of Conservation Biology

Lecturer: James Reeler

Requires integration of a number of different concepts: landscape ecology ecosystem management population genetics disturbance ecology

At several different scales: community population species local landscape

Minimum viable population size (MVP). Based on two parameters:

acceptable probability of survival time period being considered

Usually insufficient information to draw such conclusions

Smaller populations are more likely to go extinct over a given time period than larger ones

For a given set of parameters, the given MVP is highly species dependent.

Persistence of bighorn sheep (Ovis canadensis) in California.

a) Study by Berger (1990)MVP=100

b) Study by Wehausen (1999)MVP=50

Attempts to build models that predict future population trends

Depends on relationship between popn size (dependent) & weather, disease, landscape trends (independent)

Simplest model is stepwise:

where S = probability of individual surviving from t to t+1 B = average number of offspring per individual

If these variable are measured in the field, the model can integrate randomly generated stochastic events

Variation in birth rate can be set by assigning variation level

Monitoring is essential to the successful running of a reserve

Scale is important for monitoring Up to 90% of species declines are missed due

to inappropriate scale of monitoring Level of monitoring for British butterlies was

~100km2 (10km x 10km) Much larger than individual patch (habitat or

population) size As long as the species is detected within those

cells, the population is not registered as disappearing, although it may experience huge reduction s within each area

80-90% declines undetected in British butterflies (Cowley et al., 1999) Worst amongst widespread species,

Often small populations are disproportionally vulnerable due to genetic inbreeding

Franklin (1980) suggests a minimum of 50 individuals to proevent rapid loss of genetic variability

Studies on Drosophila suggest 500 as a minimum to allow for sufficient mutation to counter loss through genetic drift

Known as 50/500 rule for managing small populations Complicated by difference between full population

and the effective population (Ne) which is involved in exchange of genetic material

3 common sources of deviation from perfect population

Variance in reproductive output large variance means some genes are poorly

represented in the filial generation

δ2= variance in family size Unequal sex ratios

means some individuals cannot breed with increasing inequality, Ne goes down

Population fluctuations effectively causes generational bottlenecks that

reduce gene numbers.

Until recently conservation management meant preventing all disturbance to natural areas.

Disturbance is not exclusively anthropogenic Many areas require disturbance to maintain their

biodiversity Different reserves experience (and require) different

disturbance regimes Fynbos is a good example of a fire-disturbed ecosystem

the requires regular disturbance Savannah maintains the balance of trees and grassland

through the interplay of several disturbance regimes: fire herbivory pressure (including migration) elephants drought/flood cycle nutrient enrichment via animal excreta

Certain life cycle attributes denote plants (and some animals) that profit in a disturbance regime short life cycle (from seed to flower) allocation of most resources to reproduction long-lived soil-stored seed banks long-distance dispersal mechanisms polymorphic seeds so that some are dispersed in time

and some in space disturbance-cued germination adult plasticity, meaning that a plant can be big or

small, slow or fast growing depending on the available resources in a patch

vegetative propagation (this adaptation is selected under the pressure of mammalian herbivores, shifting dune systems or floods.

These species REQUIRE disturbance over a certain period in order to maintain biodiversity

Good knowledge of the required disturbance regimes of the conservation area is required (monitoring!)

For fynbos, burning every 13-15 years is recommended Does not mean burn EVERYWHERE once every 15 years

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Natural landscapes are a mosaic of different habitats, and different burn regimes

Older veld allows for reintroduction of species that may have been burned out

Young veld provides areas for succession to occur in natural processes

Record-keeping essential

After plants die, their nutrients are first consumed by detritivores before being returned to the soil.

During this period of mineral release, ecosystems are highly vulnerable.

Depending on rate of sprouting & repopulation compared with runoff & leaching, nutrients may be lost to the system or retained in new plants

Clearance of small blocks of vegetation tends to lose less nutrients (since they are taken up by the roots of surround plants).

Salts such as K, Mg & Na are lost first (highly soluble) although in arid environments they may form a salt crust that prevents seedling growth

Disturbance reducing a single species may cause cascade losses in other species (eg: rinderpest)

Hunting of elephants in central Africa led to increased bush encroachment, and reduced savannah species. reduction in poaching in conservation areas swung the balance the other

way, with losses of some large trees and reduction in browsing species increased poaching has led to reduction in grassland each change caused large shifts in plant and insect diversity as well as

large mammals

Some wild populations are still harvested, and in certain reserve types (biosphere reserves) areas are set aside for limited take)

Central to the idea of harvesting is the concept of sustainable yield

This is any level of harvest that can be taken from the population indefinitely without detriment to the population

From a commercial point of view, the best amount to remove would be the maximum sustainable yield

Calculation of this is based on the carrying capacity of the land, and the logistic equation for population growth

Harvest exceedsgrowth;

populationdeclines to K/2

Growthexceedsharvest;

populationincreases to K/2

b) Fixed harvest effort method

rK/4Harvest exceedsgrowth;

populationdeclines to K/2

a)Fixed quota method

Harvest exceedsgrowth;

populationdeclines to

extinction

Fixed harvest effort is a better method, but it still requires a good assessment of the carrying capacity for the species.

Assumes all individuals have equal reproductive potential, and hence does not take into account age structure of the population (in age-structured populations, MSY may be between 50 & 75% of K)

Assumes harvesting mortality is compensated by reduced natural mortality (no evidence)

Assumes no knock-on effects for interacting species (predators/competitors/prey) which may change carrying capacity of the environment

Ignores harvest rate of pre-reproductive individuals, body growth rate, etc.

This has led to development of more detailed models which describe biomass as a function of different processes (recruitment, natural mortality, etc)

Despite repeated efforts to achieve sustainable yield of Atlantic cod, stocks are still plummeting.

Island biogeography & metapopulation biology influence reserve selection and management processes

Depend on relative rates of colonisation & extinction, which in turn depend on: spatial distribution of patches suitability of patches for reproduction permeability of the space between patches mobility of species

Shift away from conservation as self-regulating systems to dynamic non-equilibrial systems has led to integration of reserves into the broader landscape

Use a management hierarchy such as the biosphere concept

Utilisation of corridors (natural and manufactured Integration of agricultural alternatives and communal

wildlife management as a means of broadening the potential gene pool and land availability (Wine & Biodiversity initiative, Campfire)

Ecosystem process is essential for population persistence, and so large scale conservation should aim to protect these systems.

Meyer (1997) nominated 7 principles for ecosystem conservation: ecosystems are open, which should lead to a focus on

conserving fluxes (flow) across ecosystem boundaries ecosystems are temporally variable & bear the legacies of

past disturbance spatially heterogeneous on a variety of scales, which is vital

for functionality most effects in ecosystems are indirect, making knock-on

effects unpredictable component biological communities must be conserved to

maintain ecosystem function although several species may perform the same function in

the ecosystem, they have different responses to biotic & abiotic environment (reduced variation in functionality in a changing environment)

humans are part of all ecosystems, and no ecosystems are unaffected by human activity.

How usefully a management policy integrates this holistic approach may depend on how impacted an ecosystem is by

human/economic activities, how well we understand the processes

Meyer (1997) cites the example of the Knowles Valley (USA) which underwent extensive logging & roadbuilding in 1950-1985 shifted sediment load from uplands to valley decreased storage capacity in valley meant much

was washed out of the catchment degraded habitat for coho salmon, which had

greatly reduced migration to the sea By replanting trees & reducing sediment loss, a

recovery programme stopped this.

Sometimes too much transformation has occurred, and it is necessary to allow short term, small scale losses to accommodate longer term restoration

Guiding principles for ecosystem management (Maltby, 1999): management objectives are a matter of social choice ecosystems must be managed in a human context ecosystems must be managed within natural limits change is inevitable management & monitoring must occur at the

appropriate scale, & use the full range of protected areas

needs to address global issues but act locally must maintain ecosystem structure & functioning should use appropriate scientific tools follow the precautionary principle needs a multidisciplinary approach.