Tag Archives: alces

On Moose Who Reproduce: To Use Or Not To Use

Guest post by Endre Grüner Ofstad

Opposing fitness consequences of habitat use in a harvested moose population (2019) Ofstad, Markussen at al., Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.13221

The Crux

At the heart of our understanding of animal behaviour is Optimal Foraging Theory. It’s related to the core concepts of population ecology, and essentially asks which life history trait a species is more concerned with – survival or reproduction. For instance, often for a herbivore, the areas where they will find the most food is also the area where the most predators will be lurking. This presents them with two options – eat lots, reproduce a lot, and die young, or eat less, reproduce less (at least per year) and live longer.

On a species level we can compare mice and elephants. Yet these differences also occur within species and populations. Some individuals are more prone to high-risk strategies, while others prefer the low-risk strategy. Which strategy is the best will depend on the prevailing environment. For instance, a situation with few predators (or hunters) will favour the more risk-prone strategy, while a strong presence of predators will favour the risk-averse strategy. Populations who experience environmental variations are expected to have a composition of strategies that varies accordingly. 

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Hvorfor er dyr hvor de er?

Image Credit: Endre Gruner Ofstad, CC BY-SA 2.0

Guest post by Endre Grüner Ofstad. English version here.

Use, selection, and home range properties: complex patterns of individual habitat utilization (2019) Endre Ofstad et al., Ecosphere, 10(4), https://doi.org/10.1002/ecs2.2695

Det essensielle

Stedene man finner dyr omtales gjerne som dyrets habitat. Habitat er et relativt vagt begrep. Hvor individ oppholder er som regel et utfall av en rekke vurderinger: hvor finner en mat, hvor unngår man rovdyr og hvor finner man noen å parre seg. Individ avveier blant disse for å maksimere hvor mange avkom de kan tilføre fremtidige generasjoner (også kalt for ‘fitness’).

Når vi skal vurdere hvilke habitat dyr befinner seg i så jobber vi som regel med habitatseleksjon. Habitatseleksjon er hvor mye et habitat blir brukt i forhold til hvor tilgjengelig det er, dvs. hva er den relative sannsynligheten for at et dyr vil bruke et habitat hvis det får muligheten. Hvor mye tid et individ velger å bruke (eller tettheten av individ) i et habitat er som regel en god indikator på hvor viktig et gitt habitat er. Habitatseleksjon blir derfor ofte brukt til å identifisere hvilke habitat forvaltningen bør iverksette tiltak.

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Why are animals where they are?

Image Credit: Endre Gruner Ofstad, CC BY-SA 2.0

Guest post by Endre Grüner Ofstad. Norwegian version available here.

Use, selection, and home range properties: complex patterns of individual habitat utilization (2019) Endre Ofstad et al., Ecosphere, 10(4), https://doi.org/10.1002/ecs2.2695

The Crux

The areas in which we find an animal is often called its ‘habitat’. Yet it’s a fairly ambiguous term. Where animals are found is usually the outcome of a range of considerations, primarily foraging, predator avoidance and mating opportunities. Animals trade-off among these in order to maximise their contribution to future generations (i.e. ‘fitness’).

When considering which habitats we most likely find animals one often works with habitat selection. Habitat selection is how much a certain habitat type is used compared to its availability, i.e. what is the relative probability that an animal will use a given habitat upon encounter. The amount of time an individual spends (or density of individuals) in a habitat is usually a good proxy for the importance the habitat to the animals. Therefore we often use this to evaluate which areas to target for management and conservation efforts.

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