Population cycles have long fascinated ecologists. Even in the most-studied populations, however, scientists continue to dispute the relative importance of various potential causes of the cycles. Over the past three decades, theoretical ecologists have cataloged a large number of mechanisms that are capable of generating cycles in population models. At the same time, statisticians have developed new techniques both for characterizing time series and for fitting population models to time-series data. Both disciplines are now sufficiently advanced that great gains in understanding can be made by synthesizing these complementary, and heretofore mostly independent, quantitative approaches. In this paper we demonstrate how to apply this synthesis to the problem of population cycles, using both long-term population time series and the often-rich observational and experimental data on the ecology of the species in question. We quantify hypotheses by writing mathematical models that embody the interactions and forces that might cause cycles. Some hypotheses can be rejected out of hand, as being unable to generate even qualitatively appropriate dynamics. We finish quantifying the remaining hypotheses by estimating parameters, both from independent experiments and from fitting the models to the time-series data using modern statistical techniques. Finally, we compare simulated time series generated by the models to the observed time series, using a variety of statistical descriptors, which we refer to collectively as “probes.” The model most similar to the data, as measured by these probes, is considered to be the most likely candidate to represent the mechanism underlying the population cycles. We illustrate this approach by analyzing one of Nicholson’s blowfly populations, in which we know the “true” governing mechanism. Our analysis, which uses only a subset of the information available about the population, uncovers the correct answer, suggesting that this synthetic approach might be successfully applied to field populations as well.

/pdf/why-do-populations-cycle-a-synthesis-of-statistical-and-5837pk5754.pdf

Why do populations cycle? a synthesis of statistical and mechanistic modeling approaches

PART I REVIEWS: 1. Dramatis personae 2. Ancestry 3. Population genetics 4. Society 5. Management 6. Infectious disease 7. Tools PART II CASE STUDIES 8. Arctic foxes 9. Island foxes 10. Swift foxes 11. Blanford's foxes 12. Red foxes 13. Raccoon dogs 14. Bat-eared foxes 15. Patagonian foxes 16. Jackals 17. Coyotes 18. Grey wolves - Isle Royale 19. Grey wolves - Yellowstone 20. Ethiopian wolves 21. Dholes 22. African wild dogs CONCLUSIONS 23. Conservation REFERENCES

The biology and conservation of wild canids

Allelic variation at seven hypervariable tri- and tetranucleotide microsatellite loci was used to determine levels of population differentiation between 14 populations of red grouse (Lagopus lagopus scoticus) in northeast Scotland, UK. Despite the potential for long-distance dispersal in grouse, and a semicontinuous habitat, significant population divergence was observed (mean RST = 0.153; P < 0.01) and an isolation-by-distance effect detected (Mantel test: P < 0.001). Examination of the spatial trend in principal component scores derived from allele frequencies among populations highlighted a barrier to gene flow that was confounding a simple isolation-by-distance effect. This barrier corresponded to an area of unsuitable habitat for grouse associated with a river system that bisected the study area. Mean genetic relatedness was higher for males than for females in all but one of the study populations, suggesting that the territorial behaviour and natal philopatry displayed by cocks have a manifold effect in generating the observed spatial genetic structure. Lower female relatedness values suggest a higher level of female-mediated gene flow, which is sufficient to prevent the loss of genetic variation from within populations and the onset of inbreeding effects. The potential consequences of local subdivision for red grouse populations are discussed.

Local genetic structure in red grouse (Lagopus lagopus scoticus): evidence from microsatellite DNA markers

Summary

1. The functional and numerical responses of two generalist raptors (hen harrier and peregrine) were studied on one moor for 6 years and on five other moors for 5 years.



2. Neither species showed numerical responses to grouse abundance. Harrier densities were highest in areas and years where their small prey (meadow pipits and small mammals) were most abundant. Peregrine densities were highest on southern study moors, probably in association with high abundance of racing pigeons.



3. For harriers preying on grouse chicks, the available data fitted a sigmoidal or type III functional response. Peregrines showed a type II response to adult grouse densities around eyries.



4. The proportion of grouse chicks taken by harriers was estimated to have been highest at densities of 67 chicks km–2 (equivalent to a mean of about 12 broods km–2). The proportion of adult grouse taken by peregrines appeared to be inversely density dependent, such that an increasing proportion of grouse was taken at grouse densities below 20 km–2.



5. In the absence of persecution, the impact of harriers on grouse populations is most likely to be greatest on moors where alternative prey and thus harriers are abundant. The question of whether harriers may dampen grouse population cycles at low grouse density is discussed.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2656.1999.00340.x

Numerical and functional responses in generalist predators: hen harriers and peregrines on Scottish grouse moors

Because populations of territorial birds are relatively stable compared to those of other animal taxa, they are often considered to be tightly regulated. However, the mechanisms that produce density-dependent feedbacks on demographic rates and thus regulate these populations are poorly understood, particularly for migratory species. We conducted a three-year density-reduction experiment to investigate the behavioral mechanisms that regulate the abundance of a Nearctic–Neotropical migrant passerine, the Black-throated Blue Warbler (Dendroica caerulescens), during the breeding season. We found that the number of young fledged per territory, territory size, and the proportion of time males spent foraging were significantly greater on territories around which neighbor density was experimentally reduced compared to control territories. Territory quality, proportion of nests depredated per territory, and male countersinging rates were not statistically different between treatments. These results indicate that i...

Experimentally reducing neighbor density affects reproduction and behavior of a migratory songbird

Red Grouse (Lagopus lagopus scoticus) show unstable population dynamics. The number shot for sport at Rickarton moor in northeast Scotland, for example, has cycled with 10-11-yr periodicity since 1946. Here, demographic and other causes of a population cycle were documented from 1979-1989, and an experiment tested the prediction that removing some cocks during the increase phase would prevent a subsequent cyclic decline. Throughout the study, sport shooting was stopped on the area where the main work was done. During 1979-1982, before the experimental removal of cocks began, numbers over the whole moor rose from a trough at the start of the study. On the control area, the cyclic peak in 1983 was followed by a decline until 1988, as predicted in advance from models derived from a previous study elsewhere. On the experimental area, enough territorial cocks were removed each spring from 1982 to 1986 to prevent the population from attaining peak densities for five successive years, and no cyclic decline occurred. The removal of cocks resulted in similar numbers of hens being lost from the breeding population. The main demographic cause of population change on control (cycling) and experimental (cycle broken) areas was variation in the recruitment of young cocks to the spring population. On the control area, recruitment was related to cycle phase and breeding success. Changes in food, nitrogen metabolism, and parasite burdens could not explain the cycle. Demographic patterns were consistent with a model in which changes in age structure affected recruitment. These and previous results refute four hypotheses as necessary causes of population cycles in Red Grouse: (1) maternal nutrition, (2) a version of Chitty's genetic hypothesis, (3) host- parasite (caecal threadworm), and (4) predator-prey relationships. The hypothesis that age structure changes and associated behavior cause cycles by affecting recruitment and, thus, population change, remains unrefuted.

https://www.jstor.org/stable/info/2265548

Experimental Prevention of a Population Cycle in Red Grouse

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Experimental Prevention of a Population Cycle in Red Grouse