Harem size should be measured by more than the sum of its parts: Phenology-based measurements reveal joint effects of intrinsic and extrinsic factors on a polygamous herbivore under non-stationary climatic conditions.
Abstract: Social behaviour is thought to be a major component of survival, reproduction, and resilience of populations. Thus, it is a key component in management and conservation of wild populations. In polygynous breeding species, group size influences the reproductive success of males and females, and hence it is essential to understand the environmental and demographic factors that shape the phenology of group size within populations. Here, we investigate harem size and its determinants using a 15-year dataset of annual harem size phenology-based metrics from a reintroduced population of wild Przewalski horses in Hortobágy National Park, Hungary. From the initial reintroduction of 21 animals in 1997, the population grew to 174 animals in 2012. During that same period, the number of harems increased from three to 23. Despite the 8-fold increase in population size, harem sizes remained stable, and variability among harems within years decreased. The annual phenological cycle of harem size was not consistent over the 15-year period, and the associated annual phenology-based metrics varied differently over the years. The best predictors of our phenology-based harem size metrics were adult sex ratio, annual adult mortality and annual mean number of harems, with some evidence that mean age of harem stallions and drought severity were contributing factors. Our findings reveal that complex interactions between demography, climate, and harem size can emerge in social animals. Taken together, our results demonstrate that intrinsic population processes can regulate group size even in the presence of non-stationary climatic conditions during periods of growth in human-introduced, semi-free ranging animal populations.
© 2024 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.
Publication Date: 2024-02-05 PubMed ID: 38322007PubMed Central: PMC10844713DOI: 10.1002/ece3.10865Google Scholar: Lookup
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Summary
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Overview
- This study examines the factors affecting harem size in a polygamous herbivore, the wild Przewalski horse, over 15 years in a reintroduced population.
- The research uses phenology-based measurements to understand how demographic and environmental factors jointly influence social group size under changing climate conditions.
Background and Importance
- Social behavior is crucial for survival, reproduction, and resilience of animal populations, making it important for conservation management.
- In polygynous species, harem or group size impacts reproductive success for both males and females.
- Understanding how environmental (extrinsic) and demographic (intrinsic) factors influence harem size over time helps clarify population dynamics.
- Phenology-based metrics focus on timing and patterns of biological events, providing insight into how harem size changes seasonally and annually.
Study System and Data
- Focus species: Przewalski horses, a polygamous herbivore originally reintroduced into Hortobágy National Park, Hungary.
- Dataset: 15 years of annual harem size data collected from 1997 to 2012.
- Population growth observed from 21 animals at reintroduction to 174 individuals by 2012.
- Number of harems increased from 3 to 23 over study period.
Key Findings on Harem Size Dynamics
- Despite an 8-fold population increase, the average harem sizes remained stable rather than growing with population size.
- Variability among different harems within each year decreased, indicating more uniform harem sizes across the population.
- The annual cycle or phenology of harem size was not consistent, showing year-to-year variation in timing and pattern.
- Different phenology-based metrics (e.g., size peaks, duration) changed differently across years, highlighting complex temporal dynamics.
Factors Influencing Harem Size
- The best predictors of harem size patterns were:
- Adult sex ratio (balance of males to females in population)
- Annual adult mortality rates
- Number of harems present annually
- Additional contributing factors included:
- Mean age of harem stallions (older or younger males may influence group size)
- Severity of drought (climatic stress affecting population and behavior)
Implications and Conclusions
- The results reveal complex interplay between intrinsic population dynamics (demography) and extrinsic factors (climate) in shaping social group size.
- Intrinsic regulatory processes (such as mortality and sex ratio balancing) can maintain stable harem sizes even during periods of population growth.
- Non-stationary climatic conditions, such as variable drought severity, also influence social structures but do not solely determine group size.
- These findings highlight the importance of incorporating both biological and environmental variables in conservation and management strategies for social, polygamous species.
- This approach could be valuable for other reintroduced or managed wild populations under changing climatic scenarios.
Cite This Article
APA
Szemán K, Végvári Z, Gőri S, Kapocsi I, Székely T, Manning JA.
(2024).
Harem size should be measured by more than the sum of its parts: Phenology-based measurements reveal joint effects of intrinsic and extrinsic factors on a polygamous herbivore under non-stationary climatic conditions.
Ecol Evol, 14(2), e10865.
https://doi.org/10.1002/ece3.10865 Publication
Researcher Affiliations
- Department of Evolutionary Zoology and Human Biology University of Debrecen Debrecen Hungary.
- Centre for Ecological Research Institute of Aquatic Ecology Budapest Hungary.
- Senckenberg Deutsches Entomologisches Institut Muncheberg Germany.
- Hortobágy National Park Directorate Debrecen Hungary.
- Hortobágy National Park Directorate Debrecen Hungary.
- Department of Evolutionary Zoology and Human Biology University of Debrecen Debrecen Hungary.
- Milner Centre of Evolution University of Bath Bath UK.
- School of the Environment, Washington State University Pullman Washington USA.
Conflict of Interest Statement
The authors declare that they have not known competing interest that could have appeared to influence the work reported in this manuscript.
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Citations
This article has been cited 1 times.- Székely T. Exploring social behaviour using Tinbergen's 4 Questions.. Biol Futur 2025 Jun;76(2):167-179.
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