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Valenzuela-Toro AM, Costa DP, Mehta R, Pyenson ND, Koch PL. Unexpected decadal density-dependent shifts in California sea lion size, morphology, and foraging niche. Curr Biol 2023; 33:2111-2119.e4. [PMID: 37116482 DOI: 10.1016/j.cub.2023.04.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 03/20/2023] [Accepted: 04/13/2023] [Indexed: 04/30/2023]
Abstract
Many marine mammal populations are recovering after long eras of exploitation.1,2 To what degree density-dependent body size declines in recovering species reflect a general response to increased resource competition is unknown. We examined skull size (as a proxy for body size), skull morphology, and foraging dynamics of the top marine predator, the California sea lion (Zalophus californianus), which have been steadily increasing over the last few decades and have approached or reached their carrying capacity in southern California.3 We show that, contrary to predictions, male California sea lions increased rather than decreased their average body size over a 46-year (1962-2008) recovery period. Larger males had proportionally longer oral cavities and more powerful bite strength, and their foraging niche expanded. Females between 1983 and 2007 maintained stable skull dimensions, but their isotopic niche was broader than contemporary males. Increased male body size is compatible with an intensification of density-dependent sexual selection for larger and more competitive individuals concurrent with an expanding foraging niche. High foraging variability among females would explain their body size stability during decades of population recovery. We demonstrate that body size reduction is not the universal response to population recovery in marine mammals and show that selective ecological dynamics could contribute to protecting populations against the increased density-dependent intraspecific competition. However, prey shifts associated with climate change will likely prevent California sea lions (and other marine mammals) from attaining these ecological dynamics, augmenting their vulnerability to resource competition and diminishing their capacity to overcome it.
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Affiliation(s)
- Ana M Valenzuela-Toro
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 130 McAllister Way, Santa Cruz, CA 95060, USA; Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, 10th Street NW and Constitution Avenue NW, Washington, DC 20560, USA.
| | - Daniel P Costa
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 130 McAllister Way, Santa Cruz, CA 95060, USA; Institute of Marine Sciences, University of California, Santa Cruz, 130 McAllister Way, Santa Cruz, CA 95064, USA
| | - Rita Mehta
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 130 McAllister Way, Santa Cruz, CA 95060, USA
| | - Nicholas D Pyenson
- Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, 10th Street NW and Constitution Avenue NW, Washington, DC 20560, USA; Department of Paleontology and Geology, Burke Museum of Natural History and Culture, 4303 Memorial Way Northeast, Seattle, WA 98105, USA
| | - Paul L Koch
- Department of Earth and Planetary Sciences, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
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OUP accepted manuscript. J Mammal 2022. [DOI: 10.1093/jmammal/gyac023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Reading CJ, Jofré GM. The cost of breeding for male common toads. Biol J Linn Soc Lond 2021. [DOI: 10.1093/biolinnean/blab040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Abstract
The potential impact of pairing on male survivorship and future breeding success in common toads was investigated between 1993 and 2014. A total of 8132 males arriving at a breeding pond in southern England were measured, weighed, individually marked and their breeding history recorded. The body condition (BC) of all males was estimated using (a) residuals from an ordinary least squares regression analysis of log10 body mass against log10 body snout-vent length (SVL; ordinary least squares) and (b) a scaled mass index (SMI), standardized for SVL. Each year each male was allocated to one of four categorical groups: (1) Paired, (2) Unpaired, and whether or not it returned to breed the following year: (3) Return, (4) No Return. The BC of both paired and unpaired males that subsequently returned was significantly higher than that of those that failed to return. Male pairing success was highest in the youngest males and lowest in the oldest. The overall cost for male common toads that successfully paired was a significantly decreased BC and survival rate. First time breeding males had a 21.2% chance of surviving and returning to breed the following year, increasing to 28.3–37.0% for those returning for up to five consecutive years.
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Affiliation(s)
- Christopher J Reading
- UK Centre for Ecology & Hydrology, CEH Wallingford, Benson Lane, Crowmarsh Gifford, Oxon, OX10 8BB, UK
| | - Gabriela M Jofré
- c/o UK Centre for Ecology & Hydrology, CEH Wallingford, Benson Lane, Crowmarsh, Gifford, Oxon, OX10 8BB, UK
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Whitlock SL, Womble JN, Peterson JT. Modelling pinniped abundance and distribution by combining counts at terrestrial sites and in-water sightings. Ecol Modell 2020. [DOI: 10.1016/j.ecolmodel.2020.108965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Kalberer S, Meise K, Trillmich F, Krüger O. Reproductive performance of a tropical apex predator in an unpredictable habitat. Behav Ecol Sociobiol 2018. [DOI: 10.1007/s00265-018-2521-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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Bishop AM, Stewart JE, Pomeroy P, Twiss SD. Intraseasonal temporal variation of reproductive effort for male grey seals. Anim Behav 2017. [DOI: 10.1016/j.anbehav.2017.10.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Temporal variation in the operational sex ratio and male mating behaviours in reindeer (Rangifer tarandus). Behav Processes 2017; 140:96-103. [PMID: 28438692 DOI: 10.1016/j.beproc.2017.04.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Revised: 03/14/2017] [Accepted: 04/18/2017] [Indexed: 11/23/2022]
Abstract
In polygynous species, sexual selection is mostly driven by male ability to monopolize access to females in oestrous. In ungulates, the operational sex ratio (OSR), i.e. the proportion of males to individuals ready to mate, varies throughout the peak rut, resulting from the temporal variation in the number of females in oestrous. But the way males adjust their mating tactics to maximise their access to females in oestrous (i.e. as OSR varies) is yet to be investigated. Using 15 years of behavioural observations in reindeer (Rangifer tarandus), we compared the relative importance of time within the rutting season (days to the peak-rut) and the OSR to explain the variation in the propensity (i.e. the frequency after controlling for the potential number of encounters) of young and adult dominant males to engage in four mating tactics: herding females, chasing other males, investigating female reproductive status, and courting females. Male-male agonistic behaviour was the most frequent mating behaviour, followed by herding. As predicted, dominant male mating tactics changed over the rutting season: first herding, then chasing other males, and finally investigating and courting females. In contrast to our prediction, we did not find support for the OSR theory. We noted some discrepancies in how young and adult dominant males adjusted their tactics during the mating season, adults being more efficient in timing and in performing their behaviour to maximise access to females in oestrous. The reported sequence of mating tactics may be more efficient than a static mating tactic to monopolize females in oestrous, regardless of the population composition.
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Trillmich F, Meise K, Kalberer S, Mueller B, Piedrahita P, Pörschmann U, Wolf JBW, Krüger O. On the Challenge of Interpreting Census Data: Insights from a Study of an Endangered Pinniped. PLoS One 2016; 11:e0154588. [PMID: 27148735 PMCID: PMC4858284 DOI: 10.1371/journal.pone.0154588] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Accepted: 04/16/2016] [Indexed: 11/18/2022] Open
Abstract
Population monitoring is vital for conservation and management. However, simple counts of animals can be misleading and this problem is exacerbated in seals (pinnipeds) where individuals spend much time foraging away from colonies. We analyzed a 13-year-series of census data of Galapagos sea lions (Zalophus wollebaeki) from the colony of Caamaño, an islet in the center of the Galapagos archipelago where a large proportion of animals was individually marked. Based on regular resighting efforts during the cold, reproductive (cold-R; August to January) and the warm, non-reproductive (warm-nR; February to May) season, we document changes in numbers for different sex and age classes. During the cold-R season the number of adults increased as the number of newborn pups increased. Numbers were larger in the morning and evening than around mid-day and not significantly influenced by tide levels. More adults frequented the colony during the warm-nR season than the cold-R season. Raw counts suggested a decline in numbers over the 13 years, but Lincoln-Petersen (LP-) estimates (assuming a closed population) did not support that conclusion. Raw counts and LP estimates were not significantly correlated, demonstrating the overwhelming importance of variability in attendance patterns of individuals. The probability of observing a given adult in the colony varied between 16% (mean for cold-R season) and 23% (warm-nR season) and may be much less for independent 2 to 4 year olds. Dependent juveniles (up to the age of about 2 years) are observed much more frequently ashore (35% during the cold-R and 50% during the warm-nR seasons). Simple counts underestimate real population size by a factor of 4-6 and may lead to erroneous conclusions about trends in population size.
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Affiliation(s)
- Fritz Trillmich
- Animal Behaviour, University of Bielefeld, Bielefeld, Germany
| | - Kristine Meise
- Animal Behaviour, University of Bielefeld, Bielefeld, Germany
- Department of Evolution, Ecology and Behaviour, Institute of Integrative Biology, University of Liverpool, Biosciences Building, Liverpool, United Kingdom
| | | | - Birte Mueller
- Center for Biology Education, University of Münster, Münster, Germany
| | - Paolo Piedrahita
- Animal Behaviour, University of Bielefeld, Bielefeld, Germany
- Facultad de Ciencias de la Vida, Escuela Superior Politécnica del Litoral, ESPOL, Guayaquil, Ecuador
| | | | | | - Oliver Krüger
- Animal Behaviour, University of Bielefeld, Bielefeld, Germany
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Piedrahita P, Meise K, Werner C, Krüger O, Trillmich F. Lazy sons, self-sufficient daughters: are sons more demanding? Anim Behav 2014. [DOI: 10.1016/j.anbehav.2014.09.027] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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