BZ3740 – Wildlife Ecology and Management

Interaction between organisms and their environment, i.e how an animal interacts with other animals and the abiotic (Physical) environment
managing wild populations, includes conservation, harvesting valuable spp, controlling pest spp, dealing with human-wildlife conflicts
Management goals
1. maintain many populations at ‘natural’ densities (biodiversity)
2. increase populations of threatened species
3. sustainably harvest populations of valuable species
4. reduce populations of unwanted species (typically invasive spp.)
5. manage populations of ‘problem species’
Human desires
some species considered important, people want to utilize wildlife, people want to interact and live amongst wildlife
Human fears
people want to live amongst wildlife but they want risks removed, big predators (elephants etc) are popular but they can be a threat to life, livestock and property, people want to live in the bush but then burning changes landscape as is needed.
Human behaviours
humans are fundamentally selfish, corruption (eg, wildlife trade, development, development approvals), actions of a few (eg arsons) impact greatly, governments follow popular opinions and quick gain
The wild world is shrinking
what used to be sustainable is not now.
Problems in wildlife management (according to graeme caughley and conrad hoskin)
1. exploiting a population while holding abundance constant- sustained yield harvest.
2. reducing abundance of population that is too dense- pest control.
3. increasing abundance of a population that is too small- threatened species management.
4. managing populations of all species in an area at ‘natural levels’ (biodiversity management).
5. dealing with humans
what are we aiming for? what is natural? current? aboriginal? pre-aboriginal? a mixture?
prehuman- millions of years to about 50,000 years ago.
aboriginal- 50,000 years ago to approx, 200 years ago
current- 220 years ago to present
5000 years ago to present – introduction of dingo (now considered native).
This impacts most decisions:burning, hunting, threatened species etc etc
where does wildlife live?
in some parts of the world, just in ‘wilderness’ areas, in other parts of the world almost everywhere. Cant just expect to only protect wildlife in wilderness and national parks as much biodiversity and threatened species now occur amongst humans in impacted areas
wild areas
becoming rare, often impacted in various ways (ferals, fragmentation, fire etc)
many species have drawn a lucky card by adapting to living within mountainous ranges, many protected areas are mountainous ranges as humans didn’t/don’t generally inhabit them
Wildlife Ecology & Management
1. Sustainable harvest of animals for human uses
2. Overexploitation of animals for human uses
3. Reduction of pest or problem animals
4. Increase in declining/threatened animals
5. Maintaining ‘natural systems’ & biodiversity
1. Sustainable harvest of animals for human uses. Why is wild life harvested?
food, clothing & materials, pets/collections, medicines, traditional beliefs. for any of these to be acceptable the harvest must be sustainable
define sustainable harvest
a harvest that can continue indefinitely forever, that is if we harvest at a rate H now, the population will replenish itself at the rate r=H, so we can go on harvesting at that rate
subtle, almost universally ignored requirement of sustainability
harvest program should not chnage the population of the harvested species in unwanted ways, for example by driving evolution of undesirable characteristics
harvest theory: 1. what is the ecological basis of sustainable harvest> 2. what effect does harvesting have on harvested populations
-effects can be demographic (short-term) or evolutionary (long-term). A population growing at a rate r can be
harvested at a rate H = r, to hold size
constant. H gives a sustained yield.

But, most wild populations aren’t growing –
they’re ‘stable’ (with stochastic fluctuations)
at ‘K’ = carrying capacity

Carrying capacity (K)
Carrying capacity (K) is simply the number of
individuals that the environment can support
(e.g., due to food/competition, habitat
limitation, predation)
to get a population to produce a harvest-able surplus…
we have to make it start increasing
population growth provoking methods
1. provide extra resources for the population. 2. remove predation, or some other constraint, on population growth. 3. reduce the population below K, to provoke a compensatory increase in the population growth. we can then harvest at the rate at which the population would otherwise grow towards K…this is how sustainable harvesting is usually done.
large initial removal (H0)
pushes numbers down, population can then be harvested sustainably at any rate where H is equal to the density-specific growth rate. Note: the initial yield from the population at K is high, the equilibrium yield will be lower.
large initial removal: density dependence
this method only works if reducing the size of a population provokes compensatory population growth, this means the sustaibable harvest depends on density dependence of population growth rates.
exponential growth
some populations (eg humans) are growing exponentially and are not density dependent, but this is rare-most wildlife populations show density dependent population and logistic (restricted) growth.density dependent population growth
density dependent population growth
initially growth is limited by births, then population goes though a rapid growth phase, then survival/fecundity is reduced due to competition as you approach carrying capacity for that environment. population growth rate is hard to determine because it requires a population growing from scratch (population recovery, introduced species and lab studies are from scratch populations). growth rate plots can also focus on recruitment rate, with a maximum recruitment rate at intermediate population size (often about half of K).
what is the Maximum sustained yield (MSY)
Assuming density dependent population growth (i.e., logistic population
growth), the MSY is about K/2. harvesting below or above this point results in lower yields due to lower recruitment rates. hill shape graph is considered a production curve
what is the best (and most sustainable) harvest rate to choose?
best strategy for variable environments is fixed proportion at a harvest level below MSY.
options for a fixed quota harvesting
MSY and 1 are too risky given uncertainty in MSY, N and K.
A SY at point 2 (approx. halfway between MSY and K) is the safest.
Offers high yield but big buffer for population. see notes image
An ecologically conservative (= safe)
approach to fixed quota harvesting:
estimate buffered SY (i.e approx 0.75 of K), this gives you a fixed yield that is hopefully sustainable, accounts for issues in estimating population size (N), carrying capacity (K), variation across seasons & years, estimating the shape of recruitment.
harvest strategy #1
fixed quota at the MSY, but it is very risky, it is safer to go for a lower SY (ie. harvest at a high recruitment rate between MSY and K). however this doesn’t really account for changes in population size through time
harvest strategy #2
fixed proportion, better than fixed quota. does not rely on knowing what the production curve looks like and allows constant assessment.adjustment of quota, more ecologically robust but still need to harvest above MSY (because K and population size can change a lot year to year), but logistically tricky because the size of the population has to be estimated before each harvest season, so that the number to be taken in that season can be set, if the population drops, the size of the harvest drops and harvesters don’t like that.
harvesting strategy #3
possible to assess harvest statistics (catch vs effort) to determine quotas based on catch-effort, requires less information on population size and demography within catch effort curve: cat (or yield): the size of the harvest taken (numbers, biomass), effort: the amount of harvesting activity (number of hunting licences issues, number of boat-days etc). Idea is that catch per unit effort (CPUE) can be used to assess population size, but: requires good data, to produce an informative catch-effort curve, need to have harvested at extremes (High CUPE-low CUPE) which is inefficient at one end and high impact on the population at the other, each level o effort should have been applied long enough to allow the population to equilibrate with it-often not true.
summary of common strategies for commercial harvest
1. fixed quota:least knowledge required, most acceptable to harvesters, most likely yo lead to exploitation.
2. fixed proportion: safest, most common knowledge required, least common method.
3. catch-effort: requires tricky data to be successful.
why sustainable harvests fail
1. aiming for the MSY, especially in variable systems, many examples of failures in fisheries.
2. over-capitilization, initial yield from a harvested population may be higher than the equilibrium yield, harvest may need to be lowered through some periods (eg fixed proportion), bu harvesters want to keep taking high yields.
3. valuing short-term gains over long term sustainability, sustainable harvest requires deferring part of a harvest to allow ongoing replenishment, for populations that replenish slowly, a strict economic argument would advocate rapid over-harvest too extinction.
4. greed, lack of regulation/enforcement, particularly doomed to fail if there is: open access to resource, species cross political boundaries (no single control), harvest is illegal. tradedgy of the commons will prevail in these cases (no use limiting harvest because if i don’t take it, someone else will).
5. harvesting different species together, severely compromises the ability to sustainably harvest any one of them, the rarer species can be driven to extinction because effort remains high even when it becomes very rare (due to more common spp).
6. the basic biology was not suitable – eg some species dont have symmetrical density dependent growth rates