population dynamics

This scientific submission on commercial kangaroo management was closely based on the literature from the industry, which proved to be a revelation in what it actually admitted about its manipulation of kangaroo population numbers. Basically, the very small number of scientists dominating the academic literature and the industry have stated (variously) that the industry artificially stimulates population growth rebound beyond normal numbers in targeted populations of kangaroos; that they then justify their industry and culls on the basis that the animals are too populous and a pest; that the Australian public would not allow the industry to continue if they did not swallow the line that kangaroos are a pest; that although the industry and population culls are justified in order to prevent damage to grasslands and erosion by overgrazing, this is in fact false, and the example is given of kangaroos even at 50 per square km making almost no impact on the land, whereas the sheep that the industry is purportedly saving the land for, devastate it. This is my second article on kangaroo science (see the other one here) and I did not go into it expecting to find such blatant snake oil passing for research among a very small cognoscenti, but here it is. I’m was surprised as you will be. Also, one final word, even if the industry is correct in saying that it artificially boosts kangaroo numbers in order to have enough kangaroos to ‘harvest’, as I say at the end, that does not apply to all populations and that does not mean that the strategy is not causing population crashes and demographic anomalies, for reasons that I raise in this article. If you think there are fewer kangaroos around, you may well be right and have a better idea than the industry itself. (This researched article by evolutionary sociologist Sheila Newman [1] was originally submitted to the South Australian Commercial Kangaroo Management Plan 2018-2022 ([email protected]) on behalf of the Australian Wildlife Protection Council on 7 October 2017.)

Contents

IS THE COMMERCIAL KANGAROO INDUSTRY ACTUALLY FARMING KANGAROOS AND AT HIGHER DENSITY THAN NATURAL?
POPULATION THEORY
Demographic brakes
Demographic accelerators
More demographic Brakes: Sexual Segregation/Gender pathways
What are the consequences of loss of sex-specific territory?
How far do kangaroos migrate? 9
ENVIRONMENTAL DAMAGE MITIGATION & ROO DENSITY: THEORY & EXPERIMENT
KANGAROO WELFARE PROPOSAL THAT WOULD ALSO REGULATE FERTILITY IN ACCORDANCE WITH CARRYING CAPACITY:
Proposal of wider definition of welfare
Refugia to be permanent and extended to harbour permanent stable populations
Public attitudes led by the industry and its scientists
Is contempt for kangaroos necessary for the commercial industry to continue business as usual?
REFERENCES

IS THE COMMERCIAL KANGAROO INDUSTRY ACTUALLY FARMING KANGAROOS AND AT HIGHER DENSITY THAN NATURAL?

The literature indicates an understanding among scientists researching in the industry, that these animals are artificially kept by hunting at greater numbers than they would be naturally, in order to both offset the impact of commercial hunting and to keep it going. The numbers are being manipulated upwards, and then the alleged spontaneous overcrowding [2] is being used to justify arguments for the need for a commercial industry and damage mitigation culling. [3] If the calculations of the program of artificial ‘management’ of kangaroo populations are correct in estimating kangaroo populations too numerous, then the management amounts to a form of farming, which is preventing kangaroos from exercising normal patterns of social organisation that would limit fertility opportunities.

“Caughley (1976, 1977) outlined the principles of wildlife harvesting. To harvest a sustained yield from a population at steady density, it must first be manipulated in some way to promote its rate of increase (e.g. reduce it below its ecological carrying capacity or supplement its resources). The second of the four theoretical principles he identified was that: “Harvesting theory rests upon populations being regulated by some combination of density-dependent reproduction and mortality. This has been described well for a number of large mammals (Fowler 1987). Harvest mortality is seen as being compensated to some extent by lowered natural mortality rates and increased fecundity rates.” (Caughley (1976, 1977) cited by Tony Pople and Gordon Grigg, (1999), “Commercial harvesting of Kangaroos in Australia.” [4]

“Even as a pest, however, kangaroos are still a resource, and they can only be that while they remain numerous, a necessity which puts an economic value on their conservation.” (Tony Pople and Gordon Grigg, (1999), “Commercial harvesting of Kangaroos in Australia,”pp.38-39. ) [5]

The notion that commercial hunting is causing increases in kangaroo populations has also been articulated in an objective evaluation:

The percentage change in the population (Appendix figure b) was plotted against the percentage of the population harvested. This was a gross test of whether the harvest was regulating growth in the population. In fact, if anything, there tended to be a positive relationship between harvest rate and rate of increase, which could be interpreted to indicate that culling at recent/present levels enhances the growth rate of the population.

This result does not necessarily mean that harvesting has a causal effect on population increase. However, harvesting does mimic some of the conditions produced by natural perturbations, such as die-off of males in drought, from which the kangaroo population is adapted to recover quickly by enhancing its rate of increase. (Penny Olsen and Mike Braysher) [6]

If real kangaroo numbers are being manipulated upwards by commercial management practices, then the commercial hunting industry will not welcome my observations about how kangaroo populations may spontaneously reduce their fertility, in the absence of shooting. These observations are more likely to serve the kangaroo conservation, animal welfare, and tourism concerns.

According to predator-prey theory, predators adapt to prey numbers. Would the kangaroo harvesting industry consider this adaptation, rather than continuing to farm? Like so many industries, it seems to want more growth, so more kangaroos and more territory: The South Australian Commercial Kangaroo Management Plan 2018-2022 indicates plans to increase the commercial kangaroo meat catchment area by formally extending it [7] and by getting more farmers to work for it by shooting kangaroos on their property, through a DEWNR regional staff program. [8]

POPULATION THEORY

The population model and assumptions in the South Australian Commercial Kangaroo Management Plan 2018-2022 seem to have a number of theoretical flaws and biases, some of which at least have been pointed out in recent research.

There seems to be an underlying assumption in the population model used (exclusively predator/prey biomass dependent) [9] that all the kangaroo species under consideration breed to the maximum (W.D. Hamilton (1964)) unless prevented from doing so by natural catastrophe, big predators and human culls for commercial or other reasons. Whilst Hamilton’s rules for inclusive fitness and Dawkins’ theory on selfish genes are very important, they should not cause a failure to investigate countervailing forces to genes seeking maximum reproduction.
Gordon Grigg (1998) has even asserted that, since the creation of the dingo proof fence, the South Australian kangaroo population would have grown 40% bigger, were it not for human culling. [10] Pople, Grigg (2000) [11] later decided that dingos ‘regulated’ kangaroos, rather than ‘limited’ them. However the exclusive model of a predator/prey biomass dependent kangaroo population did not permit the consideration of other factors regulating kangaroo populations.
The South Australian Commercial Kangaroo Management Plan 2018-2022 has also asserted that European land-use would have increased the amount of water available to kangaroos, and therefore the number of kangaroos. This has been questioned on grounds that feral animals do, but kangaroos don’t, rely on artificially created water sources. [12] European land-use may really have destroyed as many or more water sources for kangaroos as it has theoretically created. In South Australia sheep-grazing and rabbits have desertified parts of the state. [13] Desertification and competition for habitat with sheep and cattle and human activity has decreased the habitat available for kangaroos.
Demographic brakes
Outside the predator/prey model, countervailing forces to reproductive urges exist in the subtleties of endogamy (breeding within a local population) and exogamy (incest avoidance) [14] which also limit fertility opportunities, including, in some species, sexual maturation. [15] For instance, in order to attempt to breed, young male kangaroos need to leave their natal group because there is only room for one dominant male breeder and he monopolises all the females unless another mature male successfully challenges him. The dispersing young male may not find a group within his range of migration that has available females or he may fail to successfully compete for them.
Aspects of cooperative breeding may be present in kangaroos and delay sexual maturation in both males and females. This could explain some variations in breeding ages in different populations and environmental circumstances. [16] These should limit fertility opportunities in a natural ecology, i.e. one not impacted by the commercial management considerations noted above or by other major disorganising human impact, such as new roads, fences, and suburbs.

My theory is that undisturbed local populations respond to environmental cues like rainfall and soil richness by a variation in genetic algorithms for fertility. Sexual maturation and pairing is limited by the availability of territory. In humans these algorithms translate into kinship and marriage rules that vary in degree according to rainfall and other environmental cues. [17] In humans, the regulating effects of endogamy are part of mainstream French demographic theory [18] but have little profile in the Anglosphere. Extreme examples of this exist in humans – for instance royal dynasties - and other species – for instance naked mole-rats - and have the effect of consolidating territory and restricting enlargement of the community sharing that territory. [19]

Demographic accelerators

But we have abundant examples demonstrating that, because of hunting and culling, more fertility opportunities are being created for younger, smaller animals

“Commercial harvesting may affect the demography (e.g. size, growth, distribution and birth and death rates) of harvested kangaroo populations by selecting the larger kangaroos, which tend to be the older males (Allendorf et al. 2008). Commercially harvested populations may have a lower average age compared to that of unharvested populations. The average size of kangaroos in harvested populations may be lower, and populations contain a higher proportion of young animals than unharvested populations, but these differences are lessened during drought when older animals are lost from unharvested populations (Pople 1996).The sex bias (i.e. the percentage of harvested kangaroos that are male) has increased from 60-70% male to 92-97% male for red and western grey kangaroos (DEWNR 2017). The increase in sex-bias is due, in part, to some meat processing plants only accepting male carcasses. The sex bias of the euro harvest has historically been higher due to the small size of female euros, but the sex-bias has also increased from 75-95% male to 99% male (DEWNR 2017).” (South Australian Commercial Kangaroo Management Plan 2018-2022) [20]

Massive bias for shooting large males leaves remaining, smaller males, without the suppression of sexual maturation (possibly) or sexual behaviour (definitely) that those large competitive mature males would have caused. The remaining smaller males do not need to disperse from their natal group to breed. The natal groups may be so fragmented that most adult relatives have disappeared and the remaining young does and bucks may lack the normal incest avoidance due to disturbance of Westermarck relationships. [21] It is also possible that the presence of mature related males and females may delay sexual maturity or behaviour in female kangaroos, so that loss of big males and females would then also favour early breeding in young does.
Penny Olsen and Mike Braysher have also noted this effect:

“However, harvesting does mimic some of the conditions produced by natural perturbations, such as die-off of males in drought, from which the kangaroo population is adapted to recover quickly by enhancing its rate of increase.” (Penny Olsen and Mike Braysher) [22]

And the industry knows that hunting affects populations upwards:

“To harvest a sustained yield from a population at steady density, it must first be manipulated in some way to promote its rate of increase (e.g. reduce it below its ecological carrying capacity or supplement its resources).” (Caughley (1976, 1977) cited by Tony Pople and Gordon Grigg (1999) [23]

If there were really a desire to achieve smaller kangaroo populations naturally, then a number of things could be tried. Assuming that the disorganisation caused by hunting and culling is responsible for managing the population numbers upwards, we might create reliably safe areas and corridors local to various kangaroo clans in the harvesting area so that they could adapt to protect dependent young and females, encouraging the Westermarck effect, normalisation of patterns of incest avoidance and dispersal, weight, rate of maturity, sexual competition and fertility response to environment. If this succeeded it would reduce both the perceived need and the opportunity for the commercial industry as well as damaging the kangaroo’s reputation for overpopulation. These refugia could also provide a safe and permanent environment away from the massive human population expansion and landscape transformation which also uproots, scatters and kills kangaroos.

More demographic Brakes: Sexual Segregation/Gender pathways

Some other variations in population organisation can affect fertility opportunities. Examples include separate gender pathways, with 'sexual segregation' where male and female populations live apart.

“Sexual segregation is a phenomenon seen in many species, with segregation occurring along behavioural or ecological dimensions. Sexual segregation in western grey and red kangaroos in semi - arid Victoria has been the subject of intensive investigations since the last review.

[…] MacFarlane and Coulson (2005) investigated the effects of mating activity, group […] composition, spatial distribution and habitat selection on sexual segregation in western grey and red kangaroos. The synchrony and timing of mating activity was seen to influence the magnitude and timing of social segregation in these species, with mixed sex groups predominating during the breeding season. …

… Spatial segregation and habitat segregation were also seen. Although the magnitude of these types of segregation were weaker, they were both still significantly influenced by synchrony and timing of breeding.

Coulson et al. (2006) discussed sexual segregation at three levels (habitat, social and dietary) and confirmed that both size and sex influence segregation.

MacFarlane and Coulson (2009) showed that the need for males to maintain contact with other males (perhaps to develop important fighting skills, evaluate rivals and establish a dominance hierarchy) might also promote sexual segregation.

Similarly Nave (2002) reported evidence of sexual segregation in eastern grey kangaroos in Victoria.” (Review of Scientific Literature Relevant to the Commercial Harvest Management of Kangaroos http://www.environment.nsw.gov.au/resources/nature/110641Kangaroolitreview.pdf)

What are the consequences of loss of sex-specific territory?

Years ago, Glen Marshall, who was a teacher and missionary in PNG between 1960 and 1974 [24] told me that fertility shot up when churches convinced men and women to cohabit, where previously they had separate land and houses. I was later able to study this concept in detail and wrote a book about how Pacific Islander land-tenure and inheritance traditions kept populations within the limits of small islands. [25]
What effect could reduction of habitat, forced cohabitation, forcibly changed migration routes and wiped out populations have on male/female kangaroo territory and consequently on fertility opportunities?
How do we know that the female bias (recorded by Fletcher, 2006) at Tinbinburra, for instance, is not due to that area being female territory?
How far do kangaroos migrate?
Another aspect of population theory is migration.
The South Australian Commercial Kangaroo Management Plan 2018-2022 estimates red kangaroo ranges based on Croft 1991 and Pople et al 2006.[26] Should these range estimates take into account recent MT DNA studies, such as Zenger et al DNA study 2003. [27] Zenga et al look at Eastern kangaroo populations, but I note that South Australia uses the NSW model anyway. [28] Clegg et al, emphasise

“Significant genetic differentiation of mtDNA, implies demographic differentiation of the female portion of the population and demographically separated parts of the population should be managed as separate units. [29]

Underestimation of real geographical range risks skewing the estimation of population numbers by confusing seasonal or reactive population movement with permanent populations: Pople et al (2007) [30] acknowledged that temporal and spatial kangaroo population movement had been ignored in the models and it does not seem to be taken into consideration in the South Australian Management Plan yet. Pople et al did not, however, consider the discrete dynamics within local populations and their interactions with other populations within the overall area. They were looking at a commercial hunting model seeking to predict when and where populations would be grouped together and easier to harvest economically.
Effectively the counting method and population model in the South Australian Management plan seems to assume an undifferentiated ‘metapopulation’ and to ignore the local populations that actually make up that metapopulation and which have their own local characteristics of endogamy, exogamy, dispersal and philopatrie within that metapopulation.

“A metapopulation is a population of populations (Hanski & Gilpin 1991). Wright (1940) laid the groundwork for a genetic theory of metapopulations, while Andrewartha & Birch (1954, Ch.14) did the same for metapopulation dynamics: 'A natural population occupying any considerable area will be made up of a number of local populations or colonies. In different localities the trend may be going in different directions at the same time.' They emphasized the influence of dispersal on the number of patches occupied at any given time.” (Caughley, 1994). [31]

ENVIRONMENTAL DAMAGE MITIGATION & ROO DENSITY: THEORY & EXPERIMENT

Goal: […] to provide an alternative management option for reducing the damage to land condition caused by overabundant kangaroos. (The South Australian Commercial Kangaroo Management Plan 2018-2022, p.4. ) [32]

The South Australian Commercial Kangaroo Management Plan 2018-2022 seems to rely, as mentioned above, on a predator/prey, biomass dependent population theory, and to cite a small group of scientists who have apparently confirmed this theory time and again, describing how kangaroos wear down grasslands and then starve to death. One scientist not cited is ACT Ecologist Donald Fletcher, whose extensive field research failed to confirm the theory. The ACT Kangaroo Management model relies on the same literature as the South Australian Commercial Kangaroo Management Plan, and the model is one of high fertility sedentary populations that rarely migrate, grazing grasslands down to the subsoil. But, in his 2006 thesis, p. 237, Senior ACT Kangaroo management ecologist, Donald Fletcher, tested this model and found, to his surprise, that,

"The study did not provide evidence that high densities of kangaroos reduce groundcover to the levels where erosion can accelerate.

Unmanaged kangaroo populations did not necessarily result in low levels of ground cover. Groundcover had a positive but not significant relationship to kangaroo density, with the highest cover at the wettest site where kangaroo density was highest. Weather has an important influence on groundcover."

"The results from the study as a whole indicate that unmanaged kangaroo populations did not necessarily result in unacceptably low levels of ground cover." (Don Fletcher.) [33]

Grigg is also recorded virtually dismissing the environmental reason for culling kangaroos.

“Grigg strongly queries whether the cull is needed for its stated purpose - to protect sheep grazing land from the ravages caused by large numbers of kangaroos. If anything, according to the observations made by the team, sheep damage the land more than the kangaroos. For example, in an area east of Lake Frome, where kangaroo densities are as high as 50 per square kilometre and sheep numbers are comparatively low, the land is not degraded. It is in other places where sheep numbers are high and kangaroo numbers are low.” (Lowe, 1998.) [34]

KANGAROO WELFARE PROPOSAL THAT WOULD ALSO REGULATE FERTILITY IN ACCORDANCE WITH CARRYING CAPACITY:

Kangaroo welfare has been limited in the South Australian Commercial Kangaroo Management Plan 2018-2022 to two extremes: avoiding extinction [35] and how kangaroos may be killed. [36]

Proposal of wider definition of welfare

I would like to propose a much wider definition of welfare to include the well-being and preservation of the structure of the families and clans of this social animal, with a full age and sex cohort. This would restore and preserve their natural social behaviour and fertility regulation, with the associated incest avoidance, mating competition, and reduction of mating opportunity among smaller, younger males and females. It would probably also mean that age of sexual maturation (possibly physiological as well as behavioural) would be delayed. Infant survival would probably improve if kangaroos had the opportunity to experience and learn nurturing skills from experienced older kangaroos, instead of joeys being raised by very young kangaroos in fragmented populations.
Accordingly, since the kangaroo meat industry greatly favours the killing of the largest male kangaroos, the impact of this industry needs to be limited, and/or its selection preferences need to change.

Refugia to be permanent and extended to harbour permanent stable populations

Refugia have been mentioned in the South Australian Commercial Kangaroo Management Plan 2018-2022, as part of mitigating commercial harvest impacts. It seems, however, that no permanent safe places for kangaroo clans and mobs have been designated outside national parks. [37] Even the national parks are subject to population culls. I would propose that permanent and extensive refugia connected by safe corridors be designated for the welfare of kangaroos and with the purpose of allowing their populations to regain and retain their natural structure.

If commercial hunting were to persist, it would be with a much lower target ‘harvest’ and only take place in areas outside substantial refugia. Although Grigg has suggested that kangaroos don’t compete with sheep and don’t damage pasture, farmers might perceive a benefit from smaller kangaroo populations than those that have to date been cultivated by the commercial kangaroo hunting industry. Tourism would presumably benefit from the experience people enjoy in seeing healthy, confident, stable kangaroo clans and mobs undisturbed in their natural habitats.

Public attitudes led by the industry and its scientists

Public attitudes led by the industry and its scientists. Kangaroos have been given an undeservedly bad name by the commercial kangaroo industry and many of the scientific papers, as ‘pests’ in plague proportions. Yet my citations from the literature, beginning with (Caughley (1976, 1977) cited by Tony Pople and Gordon Grigg (1999), in “Commercial harvesting of Kangaroos in Australia,” show that the industry knowingly artificially stimulates those numbers by hunting. Kangaroo science writers freely use the term ‘pests’ to describe kangaroos. For instance Pople and Grigg (1999) provide a good example of what seems the cynical use of this term, [38] when we know that Grigg was unconvinced that culls are needed for their stated purpose – to protect sheep grazing land from the ravages [purportedly] caused by large numbers of kangaroos – when he says that sheep do far more damage and kangaroos little if any. [39]

Is contempt for kangaroos necessary for the commercial industry to continue business as usual?

“The main reason an industry is approved is almost certainly because of the extent to which kangaroos are regarded as a pest.” [40] (Pople and Grigg 1999)

Indeed, Australians have tended to absorb this cynical attitude as it has been handed down by the authorities and promoted by the press. Politicians implement it. The ‘pest’ epithet has excused reducing the notion of ‘welfare’ for kangaroos to whether the species might become extinct or the manner of a kangaroo’s final moments, ignoring the quality of most of its life. It has probably stimulated public contempt for kangaroos which has resulted in growing reports of mutilations and tortures, and the tendency to grant cull permits to farmers without inspecting the reasons. The public need to be properly educated to understand that kangaroos don’t normally overpopulate their ranges and also don’t damage their habitat. They also need to be given permission to enjoy and respect these attractive and social animals, which form an integral part of Australia’s extraordinary evolution and natural endowment.

ENDNOTES
[2] “Harvesting will invariably involve some injuries and protracted deaths. However, this must be weighed up against compensatory mortality, reduction in other forms of killing when an animal changes status from a pest to a resource, the quality of life for individuals in dense, unharvested populations during droughts and alternative land uses if harvesting is not allowed.” Tony Pople and Gordon Grigg,“Commercial harvesting of Kangaroos in Australia,” Department of Zoology, The University of Queensland, for Environment Australia, August 1999, p.2).
[3] “Australia's problem with abundant kangaroo species: Australia has about 50 species of marsupial mammals of the Super-family Macropodoidea. Most of them have declined in the 210 or so years since Europeans settled here, some to extinction. Some, however, have thrived to the extent that they are now among the most abundant large mammals anywhere. The abundant species, particularly the three largest species of kangaroo, are so numerous in many rural areas that they are regarded as pests, in competition with sheep and cattle for pasture which, in a dry country like Australia, is always in short supply.
The abundance of kangaroos, with their high conservation status, and the recognition that they are regarded as a serious pest by graziers gives Australian conservation agencies a problem. Not surprisingly, all Australian macropods are protected by law, as is almost all Australian wildlife. The solution to this conflict has been to issue limited permits which allow kangaroos and some of the most numerous wallabies to be shot as pests. However, most of the control is effected through permitting a regulated commercial harvest of kangaroos and wallabies for meat and for leather.
Any commercial harvest or pest destruction of wildlife is likely to be controversial, especially if the subjects are as appealing and as well known as Australia's kangaroos. That kangaroos are the most readily identified symbol of Australia, and that they are harvested by shooting, only exacerbates the concern, and it is not uncommon for there to be organised public campaigns against their commercial use. […]
[…] The individual aims of the Management Programs differ a little between the different States but, in general, all identify the need to balance land-use requirements against the necessity to ensure continuation of self perpetuating kangaroo populations of all species.” Tony Pople and Gordon Grigg,“Commercial harvesting of Kangaroos in Australia,” Department of Zoology, The University of Queensland, for Environment Australia, August 1999, p.2).

[4] Caughley (1976, 1977) cited by Tony Pople and Gordon Grigg, “Commercial harvesting of Kangaroos in Australia,” Department of Zoology, The University of Queensland, for Environment Australia, August 1999, p.5

[5] Tony Pople and Gordon Grigg , Commercial harvesting of Kangaroos in Australia, Department of Zoology, The University of Queensland, for Environment Australia, August 1999, pp.38-39.

[6] Penny Olsen and Mike Braysher, Situation Analysis Report: Current state of scientific knowledge on kangaroos in the environment, including ecological and economic impact and effect of culling, for the Kangaroo Management Advisory Committee, November 2000, p. 192.
[7] “However, within the life of this plan, new Commercial Harvest Sub-Regions may be opened, on the basis of population surveys, in areas of South Australia where commercial harvesting of kangaroos is not currently occurring. The Commonwealth Government will be advised of the quotas annually through the Quota Report before implementation.” South Australian Commercial Kangaroo Management Plan 2018-2022, p.10
[8] “Action 8: Educate DEWNR regional staff and land managers on best practice for combining the use of commercial and non-commercial techniques for kangaroo management.
Performance indicators:
8.1 Develop decision-making tools to assist regional staff in providing advice to land managers on commercial vs.non-commercial kangaroo management.
8.2 Any landholder seeking a destruction permit for more than a specified number of kangaroos (determined seasonally) within a CHMR is asked to consider using the commercial harvest option in the first instance. In such circumstances, Permits to Destroy Wildlife (Kangaroos) are only offered after the commercial harvest option has been declined.
8.3 Investigate the introduction of formal training requirements (like those undertaken by Kangaroo Field Processors) for landholders requesting a non-commercial Permit to Destroy Wildlife (Kangaroos).
8.4 Investigate alternative ways to integrate commercial and non-commercial kangaroo management options to mitigate damage to land condition.” (South Australian Commercial Kangaroo Management Plan 2018-2022, p.8.)
[9] As well as being a biomass model, this also talks of how hunting stimulates population growth, which contradicts what Grigg says in the note below re cull reducing population numbers. Simplification of population dynamics in pasture biomass model: “Briefly, changes in kangaroo numbers are modelled as a function of pasture biomass which, in turn, is determined by recent rainfall, past pasture biomass and the density of kangaroos (and livestock) consuming the pasture. Harvesting obviously reduces kangaroo numbers, but the reduced density results in higher pasture biomass and therefore higher rates of increase of kangaroos. This improvement in environmental conditions for a population, which without harvesting has no long-term trend, is a basic requirement for the sustainability of a harvest. The population can be simulated 10,000 times over a 20 year period. Each run is different as, every three months, rainfall is drawn from a probability distribution using the average and standard deviation for rainfall in western NSW and thus reflects the uncertain food supply in this arid environment. Population size is also estimated with uncertainty by aerial surveys, and so this too was drawn from a probability distribution using the average and standard deviation associated with aerial surveys (Pople 2008). The population was harvested at an annual rate of 15 percent or less if it was below a particular threshold.” (Source: Appendix 3, pp31-32, South Australian Commercial Kangaroo Management Plan 2018-2022.)
[10] “Without the annual cull, kangaroo numbers would jump by 30 to 40 per cent, he says. The dingo once kept kangaroo numbers in check. Now fences keep the dingoes out of pastoral areas. ‘We’ve become the predator instead,’ Grigg says. […]” “Grigg’s team estimates that in the 20 years from 1978-1998, the number of red kangaroos in the pastoral zone has risen from about 1 million to 1.6 million, while the number of western greys has remained steady around the 400 000 mark.” (Ian Lowe, “South Australia’s great kangaroo count,” ‘Forum’, New Scientist, 12 September 1998. https://www.newscientist.com/article/mg15921516-600-south-australias-great-kangaroo-count/).
[11] A. R. Pople, G. C. Grigg, S. C. Cairns, L. A. Beard and P. Alexander, “Trends in the numbers of red kangaroos and emus on either side of the South Australian dingo fence: evidence for predator regulation?” Wildlife Research 27(3) 269 – 276, 2000, http://www.publish.csiro.au/wr/WR99030
[12] Letnic, Mike ; Laffan, Shawn ; Greenville, Aaron ; Russell, Benjamin ; Mitchell, Bruce ; Fleming, Peter, “Artificial watering points are focal points for activity by an invasive herbivore but not native herbivores in conservation reserves in arid Australia,” Biodiversity and Conservation, 2015, Vol.24(1), pp.1-16.
[13] Gordon Grigg, “Kangaroo harvesting and the conservation of the sheep rangelands,” Keynote address, Royal Zoological Society of New South Wales conference on Kangaroos, May 14, 1988.
[14] “[Inbreeding is] a lesser problem in natural populations because mating between close relatives is uncommon and individuals often actively avoid mating with close relatives (Ralls, Harvey & Lyles 1986). Caughley, Directions in Conservation, Journal of animal ecology, 1994 Vol: 63 Issue: 2 Page: 215 -244, 1994, pp220-221. Sheila Newman, Demography Territory Law: The rules of animal and human populations, Countershock Press, 2013., Chapter 4, cites:
Marie Charpentier, Patricia Peignot, Martine Hossaert-McKey, Olivier Gimenez, Joanna M. Setchell, and E. Jean Wickings., 2005. “Constraints on control: factors influencing reproductive success in male mandrills (Mandrillus sphinx).” Behavioral Ecology 16:614–623 ’Several studies have shown that maternal relatives avoid mating with one another (rhesus macaques: Smith, 1995; red colobus, Procolobus badius temminckii: Starin, 2001; Japanese macaques: Takahata et al., 2002; and see for review: Moore, 1993; van Noordwijk and van Schaik, 2004), but less is known concerning patterns of inbreeding avoidance between paternal relatives (but see Alberts, 1999). In this study, we showed that the probability of paternity by a dominant male decreased when he was related to the dam at R = .5 (the highest possible relatedness coefficient in our study). Smith (1995) showed in rhesus macaques that the intensity of inbreeding avoidance was directly correlated with the closeness of kinship, as in the mandrills studied here.’
Some other references on incest avoidance in multiple species from the same chapter:
Hoier, S., 2003. “Father absence and the age of menarch, A test of four evolutionary models,” Human Nature, Vol. 14, No. 3, pp. 209–233, Walter de Gruyter, Inc., New York.
Cockburn A, Osmond HL, Mulder RA, Green DJ, Douvle MC, 2003. Divorce, dispersal and incest avoidance in the cooperatively breeding superb fairy-wren Malurus cyaneus. J Anim Ecol 185 72:189–202;
Griffin AS, Pemberton JM, Brotherton PNM, McIlrath G, Gaynor D, Kansky R, O'Riain J, Clutton-Brock TH, 2003. A genetic analysis of breeding success in the cooperative meerkat (Suricata suricatta). Behav Ecol 14:472–480;
Mateo JM, 2003. Kin recognition in ground squirrels and other rodents. J Mammal 84:1163–1181;
Pusey A, Wolf M, 1996. Inbreeding avoidance in animals. Trends Ecol Evol 11:201–206;
Stow AJ, Sunnucks P, 2004. Inbreeding avoidance in Cunningham's skinks (Egernia cunninghami) in natural and fragmented habitat. Mol Ecol 13:443–447;
Yu XD, Sun RY, Fang JM, 2004. Effect of kinship on social behaviors in Brandt's voles (Microtus brandti). J Ethol 22:17–22.
[15] See introduction and most chapters in Nancy G. Solomon and Jeffrey A. French, Cooperative Breeding in mammals, Cambridge University Press, 1997.
See “Chapter 4: Towards a new social theory on population density and geometric patterning” in Sheila Newman, Demography Territory Law: The Rules of Animal and Human Populations, Countershock Press, 2013, (http://catalogue.nla.gov.au/Record/6537280, https://www.amazon.com.au/Demography-Territory-Law-animal-populations-ebook/dp/B00ALE8YSA, http://www.lulu.com/au/en/shop/sheila-newman/demography-territory-law-rules-of-animal-human-populations/paperback/product-21735874.html) and Sheila Newman, The Urge to Disperse, Candobetter Press, 2012. (https://www.amazon.com/Urge-Disperse-Sheila-Newman/dp/1446784134).
[16] “Kangaroos at risk,” gives examples of variations in breeding age in different populations. http://www.kangaroosatrisk.net/2-biology--population-ecology.html
[17] “Chapter 4: Towards a new social theory on population density and geometric patterning” in Sheila Newman, Demography Territory Law: The Rules of Animal and Human Populations, Countershock Press, 2013, (http://catalogue.nla.gov.au/Record/6537280, https://www.amazon.com.au/Demography-Territory-Law-animal-populations-ebook/dp/B00ALE8YSA, http://www.lulu.com/au/en/shop/sheila-newman/demography-territory-law-rules-of-animal-human-populations/paperback/product-21735874.html) and Sheila Newman, The Urge to Disperse, Candobetter Press, 2012. (https://www.amazon.com/Urge-Disperse-Sheila-Newman/dp/1446784134).
[18] For instance, references to Jaques Dupaquier and to Massimo Livi-Bacci in Henri Leridon, "Théories de la fécondité : des démographes sous l’influence ?" Population, 2015/2 (Vol. 70) Éditeur : Institut national d'études démographiques (INED), France.

[19] An extreme human example of incestuous kinship rules is that of the Egyptian pharaohs, although the reader might recognise that all ruling classes tend to be of small numbers and to marry closely within their rank. See, on various kinship rules, including the pharaohs, Sheila Newman, "Overpopulation: Endogamy,Exogamy and fertility opportunity theory," http://candobetter.net/node/3197.
The naked mole-rat is an extreme example in another species, where the female head of the community (the queen) chooses one of her sons as her ‘husband’ and the rest of her children remain sexually immature helpers. These communities (which may contain more than 80 members) are also extremely xenophobic towards other communities of naked mole-rats. Furthermore, they are extremely inbred but very hardy. See Christopher G. Faulkes and David H. Abbott, “The Physiology of a reproductive dictatorship: Regulation of male and female reproduction by a single breeding female in colonies of naked mole-rats,” in Nancy G. Solomon and Jeffrey A. French, (eds.) Cooperative Breeding in Mammals, Cambridge University Press, 1997.
[20] South Australian Commercial Kangaroo Management Plan 2018-2022, p.25

[21] The Westermarck Effect: Towards the end of the 19th century, Finnish sociologist, Edvard Westermarck, whilst conducting research into endogamy and exogamy, discovered a phenomenon which came to be called the Westermarck effect. He was able to show that incest avoidance applied to people raised together, whether or not they were genetically related. The Westermarck Effect could also be an explanation for apparent incest avoidance in many species. Since animals (and many humans) cannot be sure of their actual DNA relationship to siblings and other clan members, it might be more accurate to attribute their incest avoidance to an avoidance of members of their species who they were brought up closely with. I discuss this in Sheila Newman, Chapter 4 of Demography Territory Law: The Rules of Animal and Human Populations, Countershock Press, 2013.
[22]Penny Olsen and Mike Braysher, Situation Analysis Report: Current state of scientific knowledge on kangaroos in the environment, including ecological and economic impact and effect of culling, for the Kangaroo Management Advisory Committee, November 2000, p. 192.
[23] (Caughley (1976, 1977) cited by Tony Pople and Gordon Grigg, “Commercial harvesting of Kangaroos in Australia,” Department of Zoology, The University of Queensland, for Environment Australia, August 1999, p.5).
[24] Sheila Newman, “Suppression of matriarchal societies and population stability in Papua New Guinea 1960-1974,” Interview with Glen Marshall, /node/4382. Although this may seem an anecdotal sort of interview, separate men’s and women’s land in Micronesia, even today, and elsewhere, is a well-established fact in anthropology.
[25] Sheila Newman, Demography Territory Law: The Rules of Animal and Human Populations, Countershock Press, 2013. This also explores the Easter Island population crash narrative.
[26]“Red kangaroos have sedentary populations that move within home ranges of variable size (typical weekly home range size may be up to 560 hectares or 5.6km 2 (Croft 1991). Red kangaroos range more widely in response to drought and can move a long way to access the better feed. Movements of up to 30km to obtain fresh pasture growth in response to rainfall have been recorded (Croft 1991). Occasional long-distance movements (i.e. >100km) of mature individuals of both sexes have been recorded (Bailey & Best 1992). Long-distance movements of red kangaroos to access better feed have also been found in the long-term aerial monitoring dataset for South Australia (Pople et al. 2006).” South Australian Commercial Kangaroo Management Plan 2018-2022, p.21.

[27] Zenger et al DNA study 2003: (Heredity (2003) 91, 153–162. doi:10.1038/sj.hdy.6800293, K R Zenger, M D B Eldridge and D W Cooper, "Intraspecific variation, sex-biased dispersal and phylogeography of the eastern grey kangaroo (Macropus giganteus)." http://www.nature.com/hdy/journal/v91/n2/full/6800293a.html
[28] “South Australia has adopted the harvest thresholds method used in New South Wales and described in the New South Wales Commercial Kangaroo Harvest Management Plan 2017-2022. The following explanation on harvest threshold setting by SR McLeod and AR Pople (2011), is taken from the NSW Commercial Kangaroo Harvest Management Plan.” (Appendix 3: Setting and applying harvest Thresholds, South Australian Commercial Kangaroo Management Plan 2018-2022, p.28.)
[29] Clegg et al, Molecular population genetics of the red kangaroo (Macropus rufus):mtDNA variation, Molecular Ecology>, 7, 679-686, (1998), p.685.

[30]“Whether the goal is conservation, sustainable use or pest control, wildlife management ideally requires regularly updated information on a population's size and distribution. Most frequently, population size is estimated from sample counts throughout a study area, but the pattern of distribution is either ignored or considered subjectively. Typically, management actions such as setting appropriate seasonal harvest limits or culling are triggered by estimates of the total population without sufficient regard to its spatial and temporal distribution. This means that management actions may be focused inappropriately, leading to wastage of money and outcomes that may be seriously suboptimal. Management actions would benefit from readily available and up-to-date information about the distribution of wildlife populations within a region, as well as the total population size. To do this, point-based sampling data need to be translated to density surfaces. Density surfaces modelled using geostatistics or habitat models have been produced from ground and airborne surveys of marine (e.g. Augustin et al. 1998; Rivoirard et al. 2000) and terrestrial (e.g. Campbell & Borner 1995; Rempel & Kushneriuk 2003) wildlife populations. However, few, if any, studies have modelled wildlife density over a large spatial and temporal extent, thereby providing local estimates of population size to inform more focused management actions.” (Pople, Phinn, Menke, Grigg, Possingham, McAlpine, “Spatial patterns of kangaroo density across the South Australian pastoral zone over 26 years: aggregation during drought and suggestions of long distance movement,” Journal of Applied Ecology 2007 44, 1068–1079)
[31] Caughley, Directions in Conservation Biology, Journal of Animal Ecology, Vol. 63, No. 2 (Apr., 1994), pp. 215-244, p. 221)

[32] Context of quote: “Widespread changes to the environment since European settlement have changed the abundance of many native species. Many species have declined in number, and some are now threatened. Other species have been able to adapt to the changes and can exploit the opportunities provided by altered habitats. These species – including kangaroos – are now present in larger numbers, or more widespread distributions, than before.
Kangaroos can be in conflict with various land uses and the objectives for which land is being managed. When this conflict occurs, kangaroos can cause detrimental impacts that may be environmental, economic, or social in nature. This plan adopts the ethic that the mitigation of environmental, economic, and social impacts of kangaroos should be allowed, provided it takes place in a manner that is humane and does not pose a risk to the long-term conservation of kangaroos.
The NPW Act provides for the destruction of kangaroos for the purposes of mitigating or preventing damage. This process is managed outside of the commercial harvest through the permit to destroy wildlife system and DEWNR’s non-commercial destruction policy, which guide staff in the issuing of non-commercial destruction permits. A landholder can apply for a permit to destroy a specified number of kangaroos when kangaroos are causing, or are likely to cause, detrimental impacts. Kangaroos culled under a Permit to Destroy Wildlife (Kangaroos) must be killed following the Non-Commercial Code.”
[33] Don Fletcher, Population Dynamics of Eastern Grey Kangaroos in Temperate Grasslands, Institute of Applied Ecology, University of Canberra, 2006 (PhD thesis), p.231.

[34] Ian Lowe, “South Australia’s great kangaroo count,” ‘Forum’, New Scientist, 12 September 1998. https://www.newscientist.com/article/mg15921516-600-south-australias-great-kangaroo-count/
[35] “Extinction is highly unlikely for this simulated population unless there is some combination of low numbers, catastrophic weather and unsustainable harvesting (i.e. much greater than 15 percent). A more useful measure of threshold performance is the probability of the population dropping to a relatively low density. This can be calculated as the proportion of the 10,000 simulation runs where the population falls below particular densities. Thresholds can be expressed in terms of standard deviations (SDs) below long-term average density for a kangaroo management zone. That way, the aim of the threshold harvest strategy is to keep the harvested population above historically low density.” (Appendix 3: Setting and applying harvest Thresholds, South Australian Commercial Kangaroo Management Plan 2018-2022, p.31.)
[36] 4.1 in South Australian Commercial Kangaroo Management Plan 2018-2022.

[37] It is not clear to me what the 'refugia' available to kangaroos are in South Australia, from this draft management plan. Are they established places where not shooting takes place, within the commercial shooting areas, or are they inferred as areas that, more or less randomly, so unpredictably, escape shooting in any month or year? Or are they simply areas that are hard for shooters to reach? From the draft review: "Commercial harvest is patchy within management regions and properties, leaving areas of unharvested refuge habitat." (p.25); "The extent of harvesting is patchy, and refugia (e.g. areas that are not harvested) or areas that are lightly harvested occur across the harvested area." Are there any reliably safe areas local to various clans in the harvesting area to which they might habituate so that they could adapt to protect dependent young etc?
[38] Here is the context: “In the management of kangaroos, their multiple status as pest, resource and national symbol are all tightly interwoven. The main reason an industry is approved is almost certainly because of the extent to which kangaroos are regarded as a pest; and their commercialisation has provided a self-funding pest control agent. Had kangaroos had no commercial value, pest control would have been a direct and continuing cost to graziers. On the other hand, their status as national symbol, with a very high conservation value, has guaranteed sufficient public interest for government conservation agencies to implement extensive monitoring and regulatory procedures which ensure that annual harvests are conservative.
The present situation is a compromise which has been responsive primarily to the opposing demands for much greater pest control on one hand and complete protection on the other.
Even as a pest, however, kangaroos are still a resource, and they can only be that while they remain numerous, a necessity which puts an economic value on their conservation.” Source: Tony Pople and Gordon Grigg, “Commercial harvesting of Kangaroos in Australia,” Department of Zoology, The University of Queensland, for Environment Australia, August 1999, pp.38-39.
[39] “Grigg strongly queries whether the cull is needed for its stated purpose—to protect sheep grazing land from the ravages caused by large numbers of kangaroos. If anything, according to the observations made by the team, sheep damage the land more than the kangaroos. For example, in an area east of Lake Frome, where kangaroo densities are as high as 50 per square kilometre and sheep numbers are comparatively low, the land is not degraded. It is in other places where sheep numbers are high and kangaroo numbers are low.” Ian Lowe, “South Australia’s great kangaroo count,” ‘Forum’, New Scientist, 12 September 1998. https://www.newscientist.com/article/mg15921516-600-south-australias-great-kangaroo-count/
[40] Tony Pople and Gordon Grigg, “Commercial harvesting of Kangaroos in Australia,” Department of Zoology, The University of Queensland, for Environment Australia, August 1999, pp.38-39.

REFERENCES

Tony Pople and Gordon Grigg,“Commercial harvesting of Kangaroos in Australia,” Department of Zoology, The University of Queensland, for Environment Australia, August 1999
Penny Olsen and Mike Braysher, Situation Analysis Report: Current state of scientific knowledge on kangaroos in the environment, including ecological and economic impact and effect of culling, for the Kangaroo Management Advisory Committee, November 2000
South Australian Commercial Kangaroo Management Plan 2018-2022
Appendix 3: Setting and applying harvest Thresholds, South Australian Commercial Kangaroo Management Plan 2018-2022
Ian Lowe, “South Australia’s great kangaroo count,” ‘Forum’, New Scientist, 12 September 1998.
A.R. Pople, G. C. Grigg, S. C. Cairns, L. A. Beard and P. Alexander, “Trends in the numbers of red kangaroos and emus on either side of the South Australian dingo fence: evidence for predator regulation?” Wildlife Research 27(3) 269 – 276, 2000
Letnic, Mike ; Laffan, Shawn ; Greenville, Aaron ; Russell, Benjamin ; Mitchell, Bruce ; Fleming, Peter, “Artificial watering points are focal points for activity by an invasive herbivore but not native herbivores in conservation reserves in arid Australia,” Biodiversity and Conservation, 2015, Vol.24(1), pp.1-16.
Gordon Grigg, “Kangaroo harvesting and the conservation of the sheep rangelands,” Keynote address, Royal Zoological Society of New South Wales conference on Kangaroos, May 14, 1988.
Caughley, Directions in Conservation, Journal of animal ecology, 1994 Vol: 63 Issue: 2 Page: 215 -244, 1994
Sheila Newman, Demography, Territory, Law: The rules of animal and human populations, Countershock Press, 2013.
Marie Charpentier, Patricia Peignot, Martine Hossaert-McKey, Olivier Gimenez, Joanna M. Setchell, and E. Jean Wickings., 2005. “Constraints on control: factors influencing reproductive success in male mandrills (Mandrillus sphinx).” Behavioral Ecology 16:614
Hoier, S., 2003. “Father absence and the age of menarch, A test of four evolutionary models,” Human Nature, Vol. 14, No. 3, pp. 209–233, Walter de Gruyter, Inc., New York.
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Mateo JM, 2003. Kin recognition in ground squirrels and other rodents. J Mammal 84:1163–1181
Pusey A, Wolf M, 1996. Inbreeding avoidance in animals. Trends Ecol Evol 11:201–206
Stow AJ, Sunnucks P, 2004. Inbreeding avoidance in Cunningham's skinks (Egernia cunninghami) in natural and fragmented habitat. Mol Ecol 13:443–447
Yu XD, Sun RY, Fang JM, 2004. Effect of kinship on social behaviors in Brandt's voles (Microtus brandti). J Ethol 22:17–22.
Nancy G. Solomon and Jeffrey A. French, Cooperative Breeding in mammals, Cambridge University Press, 1997.
Sheila Newman, The Urge to Disperse, Candobetter Press, 2012.
“Kangaroos at risk,” http://www.kangaroosatrisk.net/2-biology--population-ecology.html
Henri Leridon, "Théories de la fécondité : des démographes sous l’influence ?" Population, 2015/2 (Vol. 70) Éditeur : Institut national d'études démographiques (INED), France.

Sheila Newman, "Overpopulation: Endogamy, Exogamy and fertility opportunity theory," http://candobetter.net/node/3197.
Christopher G. Faulkes and David H. Abbott, “The Physiology of a reproductive dictatorship: Regulation of male and female reproduction by a single breeding female in colonies of naked mole-rats,” in Nancy G. Solomon and Jeffrey A. French, (eds.) Cooperative Breeding in Mammals, Cambridge University Press, 1997.
Sheila Newman, “Suppression of matriarchal societies and population stability in Papua New Guinea 1960-1974,” Interview with Glen Marshall,” /node/4382.
Caughley (1976, 1977) cited by Tony Pople and Gordon Grigg, “Commercial harvesting of Kangaroos in Australia,” Department of Zoology, The University of Queensland, for Environment Australia, August 1999, p.5).
Caughley, “Directions in Conservation Biology,” Journal of Animal Ecology, Vol. 63, No. 2 (Apr., 1994), pp. 215-244.
Tony Pople and Gordon Grigg, “Commercial harvesting of Kangaroos in Australia”, Department of Zoology, The University of Queensland, for Environment Australia, August 1999
Zenger et al, DNA study 2003: Heredity (2003) 91, 153–162. doi:10.1038/sj.hdy.6800293, K R Zenger, M D B Eldridge and D W Cooper, "Intraspecific variation, sex-biased dispersal and phylogeography of the eastern grey kangaroo (Macropus giganteus)." http://www.nature.com/hdy/journal/v91/n2/full/6800293a.html
Pople, Phinn, Menke, Grigg, Possingham, McAlpine, “Spatial patterns of kangaroo density across the South Australian pastoral zone over 26 years: aggregation during drought and suggestions of long distance movement,” Journal of Applied Ecology 2007, 44, 1068–1079.
Don Fletcher, Population Dynamics of Eastern Grey Kangaroos in Temperate Grasslands, Institute of Applied Ecology University of Canberra, 2006 (PhD thesis).
Ian Lowe, “South Australia’s great kangaroo count,” ‘Forum’, New Scientist, 12 September 1998.