Inter-specific Competition

By: Giselle RiveraManny Estrada

Nile monitors & Dwarf crocodiles in Southeastern Nigeria…

Photograph provided by: bristolzoo.org.uk Photograph provided by: www.houseofreptiles.com

• Similarities: – Food resources (i.e., crabs,

invertebrates)– Habitat (i.e., swampy rainforest

patches, forest creek banks)

• Differences: – Female crocodiles usually larger than

male.– Monitor usually larger species.– Monitors exhibit cannibalism.

Nile monitors & Dwarf crocodiles in Southeastern Nigeria…

Nile monitors & Dwarf crocodiles in Southeastern Nigeria…

• Study was conducted to find out whether these taxa were in fact competitors.

• It was found that crabs were an unlimited resource.

• Disparity in lengths – nile monitors were significantly larger than the dwarf crocodile, this in turn causes little or no inter-specific competition.

Townsend's warblers (Dendroica townsendi) & Hermit warblers (D. occidentalis)

Photo by: Jan GorzynskiPhoto by: Jan Gorzynski

Townsend's warblers (Dendroica townsendi) & Hermit warblers (D. occidentalis)• Townsend’s warblers males were

found to be more aggressive than the hermit warblers.– This was due to higher levels of

testosterone.

• Townsend’s were out-competing the hermit warblers for territory in areas of sympatry.

• Historical pattern of species replacement.

Townsend's warblers (Dendroica townsendi) & Hermit warblers (D. occidentalis)• Hybrids were used to prove that

hormonal differences were genetically based. – May have evolved through sexual

selection.

Innovative proposal for nile monitor vs. dwarf crocodile study…

• This study will be conducted to validate that there may be inter-specific competition between Varanus niloticus and Osteolaemus tetraspis by limiting their resources.

Innovative proposal for nile monitor vs. dwarf crocodile study…

Methods:• Capture and recapture technique

– Size difference not to exceed 6 inches.

• Duplicate natural habitat.• Equal number of individuals per

species.• Limit food resources (crabs)

Innovative proposal for nile monitor vs. dwarf crocodile study…

Expected Results• We expect to find inter-specific

competition amongst nile monitors and dwarf crocodiles.

• Species replacement– Due to limited amount of food

resources.

• Possible cannibalism expected.

Innovative proposal for townsend’s vs. hermit warblers study…

• The purpose of this study is to determine whether the townsend’s and hermit warbler could co-exist in a sympatric territory without a total species displacement.

Innovative proposal for townsend’s vs. hermit warblers study…

Methods• Capture and recapture

technique• Duplicate natural habitat.• Equal number of individuals per

species.• Inject the male townsend’s

warblers with estrogen.

Innovative proposal for townsend’s vs. hermit warblers study…

Expected Results• Change in townsend’s aggressive

behavior.• Little or no species displacement.• A possible outcome of this study

would be that hermit warblers might become more aggressive, but more further experimentation would be needed.

References• Luiselli, L., G.C. Akani and D. Capizzi (1999). Is there interspecific

competition between dwarf crocodiles (Osteolaemus tretrapis) and Nile monitors (Varanus niloticus ornatus) in the swamps of central Afrida? A study from southeastern Nigeria. J. Zool., Lond. 247: 127-131.

• Riley, J., F.W. Huchzermeyer (2000). Diet and lung parasites of swamp forest dwarf crocodiles (osteolaemus tretrapis osborni) in the northern congo republic. Copeia, 2: 582-586.

• Buffrenil, V., and G. Hemery (2002). Variation in longevity, growth and morphology in exploited nile monitors (varanus niloticus) from sahelian africa. Journal of Herpetology. 36: 419-426

• Pearl, C.A., M.P, Hayes, R. Haycock, J.D. Engler, J. Bowerman. (2005) Observations of interspecific amplexus between western north American ranid frogs and the introduced american bullfrog and the hypothesis concerning breeding interference. Am. Midl. Nat. 154: 126-134

• Martin, P.R., and T.E. Martin. (2001). Behavioral interactions between coexisting species: song playback experiments with wood warblers. Ecology. 82: 207-218

• Owen-Ashely, N.T., and L.K. Butler. (2004). Androgens, interspecific competition and species replacement in hybridizing warblers. Proceedings of the Royal Society of London, Series B: Biological Sciences. 271: S498-S500