Indirect evidence of density-dependent population regulation in Aponomma hydrosauri (Acari: Ixodidae), an ectoparasite of reptiles

Andrew J. Tyre, C. Michael Bull, Brigitte Tenhumberg, Neil Chilton

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

The extent to which density-dependent processes regulate natural populations is the subject of an ongoing debate. We contribute evidence to this debate showing that density-dependent processes influence the population dynamics of the ectoparasite Aponomma hydrosauri (Acari: Ixodidae), a tick species that infests reptiles in Australia. The first piece of evidence comes from an unusually long-term dataset on the distribution of ticks among individual hosts. If density-dependent processes are influencing either host mortality or vital rates of the parasite population, and those distributions can be approximated with negative binomial distributions, then general host-parasite models predict that the aggregation coefficient of the parasite distribution will increase with the average intensity of infections. We fit negative binomial distributions to the frequency distributions of ticks on hosts, and find that the estimated aggregation coefficient k increases with increasing average tick density. This pattern indirectly implies that one or more vital rates of the tick population must be changing with increasing tick density, because mortality rates of the tick's main host, the sleepy lizard, Tiliqua rugosa, are unaffected by changes in tick burdens. Our second piece of evidence is a re-analysis of experimental data on the attachment success of individual ticks to lizard hosts using generalized linear modelling. The probability of successful engorgement decreases with increasing numbers of ticks attached to a host. This is direct evidence of a density-dependent process that could lead to an increase in the aggregation coefficient of tick distributions described earlier. The population-scale increase in the aggregation coefficient is indirect evidence of a density-dependent process or processes sufficiently strong to produce a population-wide pattern, and thus also likely to influence population regulation. The direct observation of a density-dependent process is evidence of at least part of the responsible mechanism.

Original languageEnglish (US)
Pages (from-to)196-203
Number of pages8
JournalAustral Ecology
Volume28
Issue number2
DOIs
StatePublished - Apr 1 2003

Fingerprint

Aponomma hydrosauri
population regulation
ectoparasite
tick
Ixodidae
ectoparasites
reptile
reptiles
ticks
Acari
parasite
parasites
lizard
lizards
engorgement
mortality
distribution

Keywords

  • Maximum likelihood estimation
  • Negative binomial distribution
  • Population regulation
  • Tiliqua rugosa

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology

Cite this

Indirect evidence of density-dependent population regulation in Aponomma hydrosauri (Acari : Ixodidae), an ectoparasite of reptiles. / Tyre, Andrew J.; Bull, C. Michael; Tenhumberg, Brigitte; Chilton, Neil.

In: Austral Ecology, Vol. 28, No. 2, 01.04.2003, p. 196-203.

Research output: Contribution to journalArticle

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