# Individuals and populations: the role of long-term, individual-based studies of animals in ecology and evolutionary biology

> Why does following the same animals for decades matter? Two leading field biologists show how long-term studies of known individuals, from red deer and Soay sheep to great tits and baboons, have revealed how animals age, breed, disperse and live together. They also show that the longest-running studies become the most productive, yet three-year grants make them hard to keep going.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2010-clutton-brock-sheldon-individuals-populations-role-long/

## Citation and access

- **Authors:** Tim Clutton-Brock and Ben C. Sheldon
- **Year published:** 2010
- **Journal or source:** Trends in Ecology and Evolution
- **Full citation:** Clutton-Brock, T. and Sheldon, B. C. 2010. Individuals and populations: the role of long-term, individual-based studies of animals in ecology and evolutionary biology. Trends in Ecology and Evolution 25(10): 562–573.
- **DOI:** 10.1016/j.tree.2010.08.002
- **Access status:** Publisher link only
- **Where to find it:** https://doi.org/10.1016/j.tree.2010.08.002

## Tags

- **Species:** Birds > Acorn woodpecker; Birds > Bewick’s swan; Mammals > Bighorn sheep; Birds > Black-legged kittiwake; Birds > Blue tit; Mammals > Chimpanzee; Birds > Florida scrub-jay; Birds > Great tit; Mammals > Lion; Birds > Mute swan; Birds > Northern fulmar; Birds > Pied flycatcher; Mammals > Red deer; Mammals > Savannah baboon; Birds > Seychelles warbler; Mammals > Soay sheep; Birds > Song sparrow; Mammals > Yellow-bellied marmot
- **Region:** Europe > United Kingdom
- **Behaviour and ecology:** Behaviour; Competition; Dispersal
- **Methods and technology:** Descriptive statistics; Literature review; Survey instruments
- **Data type:** Existing data; Review
- **Observer qualification:** Not needed
- **Discipline:** Behaviour and ecology
- **Year published:** 2010

## Detailed keywords

- **Species:** Reviewed (examples from long-term studies of individually recognisable animals): red deer, Soay sheep, great tit, blue tit, pied flycatcher, mute swan, Bewick’s swan, fulmar, kittiwake, Seychelles warbler, baboons (savannah baboon), chimpanzee, yellow-bellied marmot, African lion, bighorn sheep, Florida scrub-jay, acorn woodpecker and song sparrow. Also mentioned: primates, ungulates, carnivores, rodents, cetaceans, bats, marsupials, seabirds, waders, waterfowl and raptors, and humans (preindustrial human populations, effects of early development). No scientific names are given in the text.
- **Location and habitat:** Mainly the United Kingdom (survey of 51 UK-based long-term studies; Soay sheep on St Kilda); the first individual-based bird studies were in Holland (the Netherlands) and Britain. Long-term studies elsewhere are discussed without locations.
- **Topics:** long-term ecological research; individual-based studies versus population-level studies; individual recognition (leg rings, natural markings, tags, dye marks, transponders); habituation to close observation; life histories; age structure, ageing and senescence; reproductive success and lifetime fitness; costs of reproduction and life-history trade-offs; population density effects; cohort effects of early development; sex allocation and sex ratio; dispersal and kinship structure; inbreeding and inbreeding avoidance; dominance, social rank and social relationships; social network analysis; cooperative breeding and eusocial societies; quantitative genetics, heritability and genetic covariance; phenotypic plasticity; responses to climate change and changes in timing of breeding; challenges of running long-term studies (funding, access, consistency of data); research productivity.
- **Statistics or models:** No new statistical analysis beyond a descriptive summary of the publication records of 51 UK long-term studies (frequencies of study duration, publications per study and per year, and probability per year of a paper in Science, Nature, PNAS or Current Biology). The review discusses animal-breeding quantitative genetic methods, network analysis, and methods for detecting evolutionary change over time (regression of breeding values on time, comparison of within-individual plasticity with population response, rates of change in standard deviations per generation, comparison with the theoretical maximum rate Rmax).
- **Data type:** Review of published research, plus a questionnaire-based survey of the publication records of 51 UK long-term (over 10 years) individual-based studies, carried out with Kelly Moyes. No dates for the survey are given.

## Synopsis

### 1. What they did

Many of the processes that shape animal populations, such as the factors controlling animal numbers and the evolution of adaptations, play out over years or decades. The authors compare two kinds of long-term animal studies: population-level studies, which track the size, structure and distribution of a population without following known individuals, and individual-based studies, which follow the lives of animals that can be recognised one by one, for example from leg rings, natural markings, tags, dye marks or transponders.

They set out six advantages of following known individuals over many years, then review how such studies have advanced six areas of ecology and evolution over the previous thirty years. Finally, they look at the difficulties these studies face and, with Kelly Moyes, survey the publication records of 51 long-term (over 10 years) individual-based studies in the United Kingdom.

### 2. What they found

Six advantages of following known individuals

- Age structure. Age affects almost all aspects of behaviour, breeding and survival, so studies that ignore it can reach misleading conclusions.

- Linking life stages. Events early in life can be connected to breeding and survival as adults.

- Social structure. Kinship and social relationships, and their effects on survival and breeding, can be measured.

- Lifetime fitness. Differences in lifetime breeding success between individuals can be measured and explained.

- Repeated estimates of selection. Selection can be measured again and again across many cohorts.

- Linking generations. Pedigrees over several generations allow the genetics of traits in wild animals to be studied.

What long-term individual studies have shown

- Development and ageing: declines in survival and breeding with age are widespread in both short- and long-lived species. Early growth, breeding history, genes and the mother’s age can all affect ageing. In polygynous species, males age earlier and faster than females; in monogamous species the difference is small or absent.

- Breeding success and life histories: a small proportion of adults often produces a high proportion of the young that join the population. In red deer, cold weather in the last two months of pregnancy is linked to low birth weights and poorer survival and breeding later in life. In Soay sheep on St Kilda, young females that breed in their first year commonly die in late winter when population density is high, especially if they are light, while in low-density years females that fail to breed survive less well than breeders.

- Sons and daughters: early studies of mammals showed that sons suckle more often than daughters and that raising sons costs mothers more. In red deer, only subordinate mothers pay these extra costs (lower survival and breeding the next year). In low-density populations, dominant mothers produce more sons. Seychelles warblers adjust the sex ratio of their young to the quality of their environment. In Soay sheep, female lambs with a male twin are born lighter than those with a female twin.

- Social groups: following individuals is usually the only way to measure dispersal. In many group-living mammals, females stay in the group they were born in and males leave to breed; in many group-living birds the reverse is more common. Females that reach breeding age in a group where their father or brothers breed often delay breeding, choose other mates or leave. Female baboons with more female relatives in their group, and with more regular social partners, tend to breed more successfully. Network analysis is beginning to describe the whole web of relationships within groups.

- Genetics in wild populations: long-term pedigrees now allow methods from animal breeding to be used on wild animals. In Soay sheep, heritability of birth weight is lowest in the years when selection on birth weight is strongest, and the genetic link between horn size and lifetime breeding success reverses across environmental conditions. In great tits, inbreeding has cumulative costs across life stages.

- Flexible responses (phenotypic plasticity): repeated observations of the same animals make it possible to tell whether changes over time, such as responses to climate change, come from individuals adjusting their behaviour or body, or from evolution.

Challenges and productivity

- Long-term studies are hard to run: remote study sites, political instability, restrictions in parks and reserves, conservation authorities increasingly sceptical of research that does not directly guide management, many data collectors, and a tension between consistent monitoring and experiments.

- The greatest single problem is keeping funding without interruptions.

- Of the 51 UK studies surveyed, the longest had run for more than fifty years. Almost all were reasonably productive, and a quarter were exceptional. The longest-running studies were the most productive: first papers usually appeared only after several years, then the yearly output rose for at least two decades, as did the chance of publishing in a high-impact journal.

### 3. What they concluded

- A relatively small number of high-quality, long-term, individual-based studies produce a disproportionate share of publications in organismal biology, especially in the highest-impact journals, because large numbers of known animals with known life histories allow new questions to be asked and answered.

- These studies also test assumptions used in studies of other species and help train many ecologists and evolutionary biologists.

- Their importance is likely to grow as understanding the effects of environmental change becomes more necessary.

- Research funding based on three-year grants is poorly suited to them: sooner or later an application fails, breaking the records of many animals’ lives and sometimes ending a study. The authors call on funders to find a better way to support long-term research without unfairly advantaging it.

### 6. Other technologies, skills or innovations

- Ways of recognising individual animals: leg rings, natural markings, tags, dye marks and transponders.

- Habituating animals to close observation; in some social bird studies, to the point where individuals can be weighed repeatedly.

- Genetic markers, which allow pedigrees to be built and open up long-term studies to more kinds of animals and mating systems.

- Social network analysis and quantitative genetic methods from animal breeding.

### 7. Implications for conservation (from the paper)

- Long-term records have given key evidence of human effects on wildlife, such as DDT on raptor fertility, oil on seabirds, lead shot on waterfowl, longline fishing on seabirds, and climate change on distribution, numbers, growth and the timing of breeding.

- Accurate predictions of population change need knowledge of age structure and the effects of age on breeding and survival.

- Long-term individual-based studies need more stable funding if they are to keep producing this evidence.

### 8. Implications for tracking (Original Wisdom's observations)

_These are Original Wisdom's observations, not the authors'._

- Much of what is known about animal life histories, social relationships and dispersal depends on recognising individual animals over many years. Being able to tell individuals apart is the foundation of these studies.

## Cite this summary

Lawrence, K. 2026. Summary of: Individuals and populations: the role of long-term, individual-based studies of animals in ecology and evolutionary biology (Clutton-Brock and Sheldon, 2010). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2010-clutton-brock-sheldon-individuals-populations-role-long/