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Case Study #1: Investigating potential biogeographic questions: Heliconius sapho and Passiflora pittieri
Question: Does the recorded distribution of both the butterfly, Heliconius sapho, and the passionflower plant, Passiflora pittieri, support the assumption that this butterfly's only larval host plant is indeed P. pittieri? In what ecosystem(s) are both found? Is there any biogeographic connection between the distributions of these species and overlapping ecosystem types?
Background: The rare butterfly Heliconius sapho is known only from Southern Belize. The only recorded host-plant for its caterpillar is the passion vine Passiflora pittieri. See: http://biological-diversity.info/psiguria.htm
Solution: Use the Map Explorer application to get a spatial view of the distribution of both species & use BERDS' Species Profiles for a more in-depth analysis of the ecosystems in which both species are found.
Time: 15 minutes
Method:
1. Select these layers from the Map Explorer:
- Ecosystems (all)
- Specimens
- Heliconius sapho leuce
- Passiflora pittieri
[Under the Specimen Layer menu, click the [Refine Selection] link. This will open a pop-up window allowing you to choose up to 4 species to display on the Map. In this case, we will select only 2 species: Heliconius sapho leuce and Passiflora pittieri .
2. On the left navigation menu of the BERDS site, click the 'Species' category, then select the 'Species Profiles' link. Search for the genus Heliconius. Click on the Heliconious sapho leuce link to display that species' profile. Repeat this process in another window for genus Passiflora pittieri.
[If you use the Firefox browser, this will allow you to have the profiles for both species open at the same time by using the right-click 'Open Window in New Tab' option.]
Now look in the profiles for both species for the 'Physiographic Information' section. There you will see a list of habitats/ecosystems in which both species have been sampled.
[Though much more time consuming, you could do such a comparison of species habitats via the Map Explorer by querying each specimen record on the map and tabulating/comparing their ecosystem information.]
Results:
The Map Explorer image shows the distribution of both species, which appears restricted to Southern Belize. Both species appear to be found in a variety of ecosystems.
[Enlarge]
A comparison of the ecosystems in which both species have been recorded from can be gleaned from the species profiles:
| Passiflora pittieri | Heliconius sapho leuce |
| IA1a(1)(a)-C - 'Tropical evergreen broad-leaved lowland hill forest, Callophyllum variant' | X |
| X | IA1a(1)(a)K-r - 'Tropical evergreen broad-leaved lowland hill forest on rolling karstic terrain' |
| X | IA1a(1)(a)K-s -'Tropical evergreen broad-leaved lowland hill forest on steep karstic terrain' |
| IA1a(1)(b)P -'Tropical evergreen broad-leaved lowland forest on poor or sandy soils' | IA1a(1)(b)P -'Tropical evergreen broad-leaved lowland forest on poor or sandy soils' |
| IA1b(1) -'Tropical evergreen broad-leaved submontane forest' | X |
| IA1b(1)K-r - 'Tropical evergreen broad-leaved submontane forest on rolling karstic hills' | IA1b(1)K-r - 'Tropical evergreen broad-leaved submontane forest on rolling karstic hills' |
| X | IA1b(3) -'Tropical evergreen broad-leaved submontane palm forest' |
| X | IA1f(2)(a)K -'Tropical evergreen broad-leaved alluvial forest on calcareous soils' |
| IA1g(1)(a) -'Tropical evergreen broad-leaved lowland swamp forest' | IA1g(1)(a) -'Tropical evergreen broad-leaved lowland swamp forest' |
| X | IA2a(1)(a)K-s -'Tropical evergreen seasonal broad-leaved lowland hill forest on steep karstic terrain' |
| X | IA2b(1)K-s -'Tropical evergreen seasonal broad-leaved submontane forest on steep karstic hills' |
| SPA(1) - 'Agriculture: non mechanized agricultural land uses including unimproved pasture' | SPA(1) - 'Agriculture: non mechanized agricultural land uses including unimproved pasture' |
Conclusions: Both species appear to have a tolerance for a wide variety of ecosystem types. Both spp. occur in a variety of forest ecosystems on a variety of soils and altitudes. There are a larger number of records for Heliconius sapho leuce, which can probably be related to the fact that the butterfly is conspicuous and easy to identify, while the passion vine is non-descript and difficult to find. Addition of new data records to the BERDS datasbase is likely to help refine this analysis.
While a variety of forest ecotypes have been reported as habitats for both species, both spp. have also been found in areas characterized by non-mechanized agriculture. Agricultural habitat seems inappropriate for species that otherwise have such clear ties to forest habitats. However, one should remember that many fragments of original forest tracts are often left standing within a non-mechanized agricultural landscape. it would seem apparent that both species can maintain themselves in such a fragmented landscape.
While both species have a largely overlapping distribution (supporting the idea that the butterfly is indeed dependant on the Passiflora pittieri vine), it is interesting to note that there are records for Heliconius sapho from the Cayo District a little further north whereas there are no records for Passiflora pittieri from this area.
There are several conclusions that can be loosely drawn from this:
- Passiflora pittieri also occurs in the Southern Cayo district, but it simply has not been found there yet.
- There is an alternative larval host plant for Heliconius sapho leuce, as yet unidentified.
- Heliconius sapho leuce is to some extent, a migratory species and those specimens found more northerly in Cayo District are a result of individuals dispersing outside their normal distributional range.
Other actions needed: Based on BERDS data, some doubt could begin to be cast on the original assumption that Passiflora pittieri is the only larval host plant for Heliconius sapho leuce - actual observed data indicates some areas where the two species are not found together. To provide further backing for such a theory, one would need to continue collecting data for both species and attempt to locate Passiflora pittieri in the Cayo district. Specifically, one needs to pay attention to the collection/observation of Heliconius sapho leuce individuals outside their normal range.
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