Habitat selection 1 Flashcards
Definition of habitat
means different things at different times.
Partridge (1978):– `the conglomerate of physical & biotic factors (e.g. shade, humidity, prey items, nesting sites) that together make up the sort of place in which an animal lives’
Habitat quality, particularly resource availability & exposure to predators likely to affect survival & reproductive success.
How to measure habitat use?
Variations in the species size, appearance, behaviour and distribution determine measurement method
Sampling at different sites e.g. quadrat – easy if organisms do not move widely or escape (e.g. snails). Either choose different habitats to sample, based on prior classification or measure habitat components at each site.
Less easy if organisms can avoid/escape capture. Sampling efficiency. Observation from a distance – focal observations + habitat recording. Bias? Conspicuous/cryptic individuals? Inaccessible habitat?
Is it necessary to identify individuals? Tagging etc.
Calls, tracks and signs, traps and camera traps, TLV, telemetry, thermal imagery. Utilised where human observation can displace a species e.g. deer preferences can be observed via frequency of damage observed in different monoculture tree plantations white tailed deer (Horton 1964) potential bias: deer may not eat some tree species and therefore leave no damage to be observed, damage may not be caused by deer, damage may be caused by different individuals
Laboratory or mesocosm study of importance of particular habitat elements
Recording and analysing (1)
Time spent in different habitat types hedgerow, mixed woodland, scrubland (scale of habitat – macrohabitat e.g. woodland, mesohabitat e.g. woodland glade, microhabitat e.g. understorey.
Multiple records/sightings overlaid on habitat map (e.g. using GIS).
Use of heatmapping for large species e.g. distribution of female grey seals during pupping season
Use of radiotagging can be effective for small animals
such as fish – as Lucas and Bubb (2014) did to study Grayling fish in streams
Principal component analysis can be used to compare multiple variables simultaneously using means and SEs overlaid.
See Lucas and Bubb (2014) Grayling habitat analysis in notes.
Recording and analysis (2)
Bias? Many records from a few individuals vs a few records from many individuals? Shift in habitat according to changing requirements & constraints?
How do different sub-populations in different localities utilise their habitat differently?
How does seasonality affect habitat use?
Organisms tend to be associated with particular habitats.– chance or choice?
If choice shaped by natural selection, organisms should choose habitats that increase their reproductive success.– Evidence?
If all individuals choose the best places there will be competition
– How will this affect their distribution?
Considerations
- Limited &/or patchy resources & competition
– some areas have denser food availaility/ nesting sites etc.
- Young, often leave natal area to avoid competition with parents and may have to search to find somewhere suitable -by trial and error or innate sense
- Areas good for feeding may not be good for nesting, sleeping etc.
- Animals may therefore move according to changing requirements & constraints.
Habitat preferences
Selection should favour mechanisms of active habitat preference given its potential selective advantages
Habitat associations due to:
1) random dispersion & differential mortality
2) preference for places likely to enhance reproductive success such as the presence of food/camouflage.
1) random dispersion & differential mortality
E.g. plants, zooplankton? Patchy distribution can result from this. Usually organisms with small body size, weak motibility, low sensory capacities.
2) preference for places likely to enhance reproductive success such as presence of food/camoflage.
Possible for independently mobile animals only?
Maybe not, even for very small, easily transported animals, sensory processes and responses over short distances maybe sufficient to enable v. local response
E.g. Red abalone Haliotis rufescens (gastropod) larvae(marine plankton) have 1-week food resource for development; settle only on the right type of coralline algae on which they feed. Chemosensory response allows them to detect molecules specifically associated with their algal food source to make preferential movements to feeding areas. Behaviour and habitat choice extends beyond vertebrates!!
(Morse & Morse 1984)
Demonstration of habitat preferences through choice experiments
e.g: establishment of new hives by honey bee swarms(Lindauer 1961):
– late spring - old queen leaves hive with c. ½ her colony.
– swarm flies to a nearby vantage point
– scout bees prospect for new sites
– Return & dance to indicate location & suitability of site.
– experiments show that new sites were chosen based on:
protection from weather
size (just big enough for swarm)
distance from original hive (prefer farthest of otherwise equivalent sites - reduce competition).
Familiar habitat?
Are the bees choosing the ‘best’ site – or just a new site that is similar to the old one?
Familiar habitat may provide template for locating new sites.
Familiarity can be learned
But - if adaptive habitat preferences have evolved by natural selection we must expect some evidence for heritable preferences independent of experience
Familiar habitat example: habitat preference in prairie deer mice
e.g. Habitat preferences in prairie deer mice (Peromyscus maniculatus) (Wecker 1963) tested if captive mice reared in woodland/grassland would choose to live in grassland as their wild counterparts prefer.
The experiment found that captive-bred mice would always choose grassland regardless of their rearing habitat and therefore expressing heritable preference. Locations of the mice were recorded on automatic data loggers that captured a record of mice as they passed – nowadays we would probably use camera traps for this purpose.
Is habitat preference truly adaptive?
If habitat preference is truly adaptive, we should expect it to increase the animal’s reproductive success. Few studies have demonstrated this directly. Several have shown that preferences are associated with enhanced survival or performance = indirect evidence for a reproductive benefit.
Feeding skills and habitat choice in tits
Tits appear to show habitat selectivity.
Coal Tits are native to coniferous regions and Blue tits deciduous. In an experiment by Partridge (1974) both species chose to spend more time in synthetic trees similar to those in their native habitat.
Partridge then carried out a feeder test (1976)
The experiment compared Blue Tits which inhabit deciduous trees and coal tits which inhabit coniferous trees. The different tree types require different feeding methods – therefore the right habitat should result in greater feeding success.
Research found that birds tended to do best (greater % success, or took less time to find food) on feeders appropriate to their habitat.
When wild birds were compared to hand-reared birds a difference in behaviours was observed that shows birds chose feeders more similar to their wild natural habitat
Grey seal breeding colonies: habitat effects
– fine scale habitat (pools of water & access) affect female pupping site choice (thermoregulation) Redman et al. (2001), Twiss et al. (2000, 2001, 2002)
–Fine scale habitat affects female breeding success:– Females in ‘better’ habitat invest more in offspring. Females are prone to overheating due to poor thermoregulation on land and therefore ‘better’ habitats tend to have access to pools of water to cool off without the need to leave their pups to cool off in the sea
Twiss et al. (2000), Pomeroy et al. (2001).– ‘Better’ habitat = lower pup mortality. Twiss et al.(2003)
