Specialized Interaction Decreases in Tropical Latitudes

Benjamin FieldsJulia FrederickCecilia Ireland

Christina KirkmanNeomi Sanghrajka

IntroductionLatitudinal Specialization Debate

Tropics vs. Temperate RegionsMutualism of plants and animal

pollinators/seed dispersersSpecialization with regard to latitudes,

contemporary vs. past climate, regional plant diversity

Latitudinal specialization gradient reversed �relative to latitudinal diversity gradient

Latitudinal Specialization Gradient1st Step: Gathering of global data set comprising a total of

282 quantitative pollination (red) and seed dispersal (blue) networks ranging in absolute latitude from 0° to 82°

2nd Step: Comparison of the mutualistic interactions between the pollinators and seed dispersers and the plants they interact with.

Pollinators shown on top, plants on bottom

generalized pollination network withfunctionally redundant pollinators

specialized pollination network withfunctionally distinct pollinators

The specialization of the interacting species was estimated by assessing patterns of niche partitioning and resource overlap among pollinator or seed disperser species.

Recent advances in the analysis of quantitative interaction networks show that network-wide interactions are more specialized in species-rich tropical communities. This idea is challenged by the authors of this article and the reverse is proved about the mutualistic interactions involving mobile pollinators and seed dispersers in the tropics and non-tropics.

Effects of Climate & Plant DiversityPast climate stability and contemporary climate

have been thought to influence biotic specialization.Past Climate Stability

reflects the temporal stability of local communitiesshows the available time for coevolution

Contemporary ClimateCumulative annual temperature is closely related to

evapotranspiration.Could be mediated by increases in plant diversity in

warm climates because it would reduce relative abundances and densities of resource species

Seed dispersal networks increased with increasing climate-change velocity.In regions with more stable climates seed dispersal

systems have become more generalizedPollination networks were not affected by the

climate-change velocity.Contemporary climate effect is much stronger

thanthat of past climate stability.

Current conditions have stronger influences associated among consumer and resource species in mutualistic networks.

Network specialization decreases with increasing plant diversity both regionally and locally.

The latitudinal gradient is even stronger than the overall plant diversity gradient with respect to the diversity of animal-pollinated flowers and animal dispersed fruits.Increasing plant diversity in the tropics is

associated with: a wider range of resource traits a larger number of distinct pollination systems

A key feature of the generalization of consumer species in mutualistic networks is high resource diversity.

Influence of Guild StructureGuild: a group of species that use the same

resourcesNot necessarily in the same niche

Species in the tropics are of a different guild than those in temperate regions.

The inter-species relations of the tropics appear to be more generalized than those of temperate regions.Because the way tropical communities function,

more species interact with more species.

Influence of Guild StructureFrugivores of the tropics disperse a more diverse

group of seeds than do the omnivores of the temperate regions.Fruit available year-round (due to the warm

climate).Diet of fruit has more species richness in the tropics.

Tropical pollinators live longer than those found in temperate climates. They have a larger window of time to pollinate more

kinds of plants.Some pollination is redundant.

Conclusions

Red: PollinationBlue: Seed dispersal

Absolute latitude [degrees]

ConclusionsEvolution will cause

In the Tropical EcosystemsIn the Temperate EcosystemsRelationship to the Graph

Take Home MessageThe pattern found was that the specialization

of both pollination and seed dispersal networks decreased as the regions got closer to the tropics.

Works CitedKissling, W.D., Bohning-Gaese, K., and Jetz, W.

(2009). The global distribution of frugivory in birds. Glob. Ecol. Biogeogr. 18, 150–162.

Schleuning et al., Specialization of Mutualistic Interaction Networks Decreases toward Tropical Latitudes, Current Biology (2012), http://dx.doi.org/10.1016/j.cub.2012.08.015

Scott Freeman. Biological Science, Fourth Edition. San Francisco: Pearson Education, Inc. 2011.