Author’s Intent Definition of Ecological Traps What is a source-sink system? Ecological Trap Models-Battin ETM-Robertson and Hutto Why is there so little evidence for E.T.? Battin’s Review of Evidence for E.T. Empirical Evidence: Indigo Buntings Four Questions for Conservation Biologists

and Managers Work Cited

To inform conservation biologists and managers of the impact of ecological traps.

To incorporate the distinction between habitat selection and habitat quality into management decisions.

More rigorous and thorough methodology needs to be developed to study ecological traps. To be able to distinguish trap habitat from variables that could compensate for traps.

Ecological trap: a low-quality habitat that is preferred over other available superior higher-quality habitats. A sink habitat that is preferred instead of avoided.

Another definition to link ecological trap theory to source-sink theory: “low in quality for reproduction and survival (that) cannot sustain a population, yet….is preferred over other available, high-quality habitats” (Donovan & Thompson 2001).

Ecological trap theory predicts that the presence of a trap will drive a local population to extinction.

Ecological traps may operate at a variety of temporal and spatial levels.

Unfortunately, they are difficult to determine and to distinguish from sinks.

Humans have accelerated the presence of ecological traps due to high modification of habitat.

Ecological traps are also present in pristine areas.

•A system in which there are two habitats: one of high quality (source) and one of low quality (sink). In a source population the population growth rate is positive but it is negative in a sink population.

•The presence of poor habitat is neutral/beneficial only when the abundance of poor habitat is higher than superior quality habitats.

Four models: Two well known models:› Ideal Despotic aka Ideal Free Distribution:

Habitat suitability declines as population density increases.

When applied to breeding-habitat selection it assumes that all individuals in the same habitat have the same reproductive success.

› Ideal Preemptive: Similar to IFD but incorporates individual

reproductive success. Potential breeding sites differ in terms of

their expected reproductive success. Individuals will always choose the best

breeding site.

None of the models incorporate age or “floaters”.

Three models are based on generalized life history traits of some group of terrestrial vertebrates (birds, or mammals).

The fourth model is less specific and uses a highly generalized animal.

Model Assumptions:› None is spatially explicit› Animals have immediate and complete

knowledge of habitat attractiveness (but not habitat quality)

› There is no cost to moving among patches

Ecological trap model conclusions:› Traps usually lead to extinction› Initial population size is important to

determine the fate of a “trapped” population› A threshold proportion of trap habitat exists in

the landscape. Implications? What determines the threshold level?

› Negative effects on reproduction or adult mortality can lead to traps.

› A continuum exists between source-sink theory and ecological traps. This continuum is based on the relationships among habitat quality, habitat selection and habitat availability.

Two types of ecological traps: › Severe: individuals exhibit a preference for

one habitat over another› Equal Preference: exhibit equal preference for

both habitats Traps occur via three mechanisms:

› 1) an increase in attractiveness of a habitat in the absence of a change in its suitability.

› 2) a reduction in habitat suitability without a loss in attractiveness

› 3) a simultaneous increase in the attractiveness and reduction in suitability of a habitat.

Traps might be rare or difficult to detect or both.

Researchers maybe are not actively searching for traps.

Results are published but the authors fail to recognize that their data supports ecological trap theory.

Scientists tend to analyze their results within a source-sink framework because ecological traps are less well known.

Animals assess the suitability of habitats indirectly. In the case of traps, the attractiveness of a habitat becomes uncoupled from its suitability for survival and reproduction.

The result is a low quality habitat seen as more attractive than a higher quality habitat.

What happens to an animal whose behavior is shaped by exposure to one set of conditions and is suddenly faced with a new/novel condition?

Evidence shows a negative relationship between habitat selection and habitat quality.

Literature review of studies that included two habitats and data on habitat selection and habitat quality. Animals also must have been able to move between the two habitats.

Battins results: 13 studies, 12 of which on birds (yay Dr.Katti!).

Background: › 2 nesting habitats: City

and exurban areas.› Higher density of hawks in

city compared to exurban area.

› Nesting begins earlier in the city with larger clutches.

Trap: Nesting mortality is much higher in the city (50%) compared to exurban (5%).

Why? › Trichomoniasis

2 habitats: grazed and ungrazed sites in a pine-oak woodland.

Background: Towhees were more than 40% more abundant in ungrazed site.

Trap: Pristine habitat-ungrazed because birds in the grazed habitat fledged over 4.5 times more offspring.

2 habitats: high canopy cover vs. low canopy cover

Preferred habitat: high canopy cover.

Trap: Higher nest predation in high canopy versus low canopy cover. The latter has a thicker understory that shields nests from nest predators (such as striped skunks).

Two nesting habitats for American Robins (Turdus migratorius): Lonicera mackii and Rhamnus cathartica vs. native species.

Background: American Robins used the exotic species for nesting habitat more so than native species.

Trap: Nesting success is lower in the two exotic species.

Due to human activity many edge habitats are created.

These anthropogenic edges concentrate nest predators.

Indigo buntings respond to habitat cue to breed in this dangerous environment

Experiment manipulated habitat shape.

Buntings preferred edgy patches.

Buntings fledged fewer young per pair in edgy patches than rectangular patches.

Indigo Buntings

1) Where are ecological traps most likely to occur?

2) What species are most likely to be vulnerable to traps?

3) How do we identify an ecological trap?

4) How do we incorporate the ecological trap concept into conservation planning?

Traps can occur in a broad range of habitat types.

Traps can be caused by human activity (indirectly and directly).

Traps can occur in pristine habitats and areas were human influence is inconsequential.

Traps occur at a variety of spatial scales: ranging from landscape to within-patch gradients to small scale sites.

Considering the enormous variety of locations and difficulties with detection, it is no surprise that there is not a recipe for ecological trap detection.

Characteristics

Landscape

High ratio of trap to source habitat

Rapid pace of landscape change

High rate of exotic species invasion

Organism

Slow rate of evolution

Low capacity for learning

Low within-population variation in habitat-selection traits

No behavioral adaptations to change

Low level about knowledge of landscape

Reliance on indirect habitat-selection cues

Low population size

Cyclical population fluctuations

Ecological traps can be viewed as an evolutionary lag-animals haven’t yet evolved mechanisms to respond properly to a changed environment particularly regarding habitat.

Traps are ephemeral as populations will either adapt to the trap, outlast it, or go extinct.

To determine an organism’s vulnerability one must consider their ability to adapt to changes in the quality of habitats.

The severity of a trap is determined by the rate of learning and rate of population decline.

Natural philopatry is a superior method for trap avoidance.

1) Determine the habitat quality of two different nearby habitats. 2) Determine if the habitat of lower quality is preferred. 3) Determine that the trap’s population growth rate is negative.› 1)Assess habitat quality-measure reproduction› 2) Assess habitat selection-measure animal abundance.› 3) Assess population growth rate using long-term mark-

recapture methods.

Trap = high abundance and lower reproductive output compared to a nearby habitat. Negative population growth rate. Can have a higher density than in nearby superior habitats.

Issues: Habitats that appear to be traps at high population density and low habitat quality but the effect disappears when densities are low.

Even if we can accurately assess habitat quality and habitat preference, the preservation of high quality habitats may not be enough for the species to thrive.

Even if the quantity of traps is low, it is still represents a threat to population survival because it is the preferred habitat.

Mitigation efforts: increase the quality of trap habitats or decrease the attractiveness of trap habitat.

Hunting can transform high quality habitats into traps.

Current population modeling software is not sophisticated enough to incorporate ecological traps. Models must incorporate both habitat attractiveness and quality separately. Models also need to allow habitat selection as animals search for the most attractive habitats.

Managers must understand the differences between ecological trap theory and source-sink dynamics.

Battin, J. 2004. When good animals love bad habitats: ecological traps and the conservation of animal populations. Conservation Biology 18:1482-1491.

Donovan, T. M., and F. R. Thompson III. 2001. Modeling the ecological trap hypothesis: a habitat and demographic analysis for migrant songbirds. Ecological Applications 11:871-882.

Pulliam, H. R., and B. J. Danielson. 1991. Sources, sinks, and habitat selection: a landscape perspective on population dynamics. The American Naturalist 137:S50-S66.

Robertson, B. A., and R. L. Hutto. 2005. A framework for understanding ecological traps and an evaluation of existing evidence. Ecology 87(5):1075-1085.

Witherington, B. E. 1997. The problem of photopollution for sea turtles and other nocturnal animals. Pages 303-328 in J. R. Clemmons and R. Bucholz, editors. Behavioral approaches to conservation in the wild. Cambridge University Press, Cambridge, UK.