Paleoecology

Paleoecology provides a context for understanding extant interactions and community structure. Although most paleoecological study has focused on biogeo-graphic patterns (e.g., Price 1997), fossils also reveal much about prehistoric species interactions and community structure (Labandeira 1998, Labandeira and Sepkoski 1993, Poinar and Poinar 1999) and even the consequences of prehistoric changes in climate (Wilf and Labandeira 1999, Wilf et al. 2001) or other disturbances (Labandeira et al. 2002). Similar morphological features of fossil and extant organisms imply similar functions and associated behaviors (Boucot 1990, Poinar 1993, Scott and Taylor 1983), helping to explain fossil records as well as to understand long-term patterns of community change.

The fossil record contains abundant evidence of functions and behaviors similar to those observed currently. For example, haustellate mouthparts of proto-Hemiptera suggest early appearance of feeding on plant sap (Labandeira and Sepkoski 1993, Scott and Taylor 1983). A fossil termite bug, Termitaradus protera, in Mexican amber has the same morphological modifications as its extant congeners for surviving in termite colonies and therefore can be assumed to have had similar interactions with termites (Poinar 1993). Dental structure of Upper Carboniferous amphibians suggests that most were predaceous and many were insectivorous (Scott and Taylor 1983).

Evidence of consistent species roles suggests that host selection behaviors and other species associations within communities have been conserved over time— the behavioral fixity hypothesis (Boucot 1990, Poinar 1993, Poinar and Poinar 1999). Association of potentially interacting taxa in the same deposits and anatomical evidence of interaction are common. For example, evidence of wood boring, perhaps by ancestral beetles, can be found as early as the Upper Carboniferous (Scott and Taylor 1983). Bark beetle galleries and termite nests, complete with fecal pellets, in fossil conifers from the early- to mid-Tertiary demonstrate a long evolutionary history of association between these insects and conifers (Boucot 1990, Labandeira et al. 2001). Some vertebrate coprolites from the Upper Carboniferous contain arthropod fragments (Scott and Taylor 1983). The presence of fig wasps (Agaonidae) in Dominican amber suggests cooccurrence of fig trees (Poinar 1993). Many fossil leaves from as early as the Upper Carboniferous show evidence of herbivory similar to that produced by modern insects (Boucot 1990, Labandeira 1998, 2002, Scott and Taylor 1983).

Boucot (1990) reported a unique example of an extant insect species associated with extant genera in an Upper Miocene deposit in Iceland. The hickory aphid, Longistigma caryae, occurred in the same deposit with fossil leaves of Carya (or Juglans), Fagus, Platanus, and Acer. This aphid species survives on the same tree genera in eastern North America, providing strong evidence for long-term association between this insect and its hosts.

Demonstrated interaction between pairs of species is less common but provides more convincing evidence of behavioral constancy (Fig. 10.7). Gut contents from arthropods in Upper Carboniferous coal deposits indicate herbivorous, fun-givorous, or detritivorous diets for most early arthropods (Labandeira 1998, Scott and Taylor 1983). Mermithid nematodes commonly parasitize chironomid midges, usually castrating males and causing diagnostic changes in antennal morphology. A number of chironomid males from Baltic and Dominican amber show both the altered antennal morphology and the nematode emerging at the time of host death (Boucot 1990, Poinar 1993). Parasitic mites frequently are found attached to their hosts in amber. Phoretic mites associated with their beetle or fly hosts are relatively rare but occur in Dominican amber (Poinar 1993). Similarly, staphylinid beetles commensal in termite nests have been found with their termite hosts in Dominican amber (Poinar 1993).

Surprisingly few examples of demonstrated mutualistic interactions are preserved in the fossil record (Labandeira 1998,2002). Scott and Taylor (1983) noted

Mermithid Nematode Chironomids

| Evidence of parasitism of extinct insects. A: Fungal synnema (spore-bearing structure) protruding from the body of a Troctopsocopsis sp. (Psocoptera) in Dominican amber. B: Two allantonematid nematodes emerging from a chironomid midge in Dominican amber. C: Parasitic nematodes radiating from a fly trapped in Dominican amber. From Poinar and Poinar (1999) with permission from Princeton University Press. Please see extended permission list pg 571.

| Evidence of parasitism of extinct insects. A: Fungal synnema (spore-bearing structure) protruding from the body of a Troctopsocopsis sp. (Psocoptera) in Dominican amber. B: Two allantonematid nematodes emerging from a chironomid midge in Dominican amber. C: Parasitic nematodes radiating from a fly trapped in Dominican amber. From Poinar and Poinar (1999) with permission from Princeton University Press. Please see extended permission list pg 571.

that spores of Upper Carboniferous plants had a resistant sporoderm capable of surviving passage through animal guts, suggesting that herbivores may have served as agents of spore dispersal. An Upper Carboniferous arthropod, Arthro-pleura armata, was found with pollen grains of a medullosan seed fern attached along its posterior edge at the base of its legs. This species could have been an early pollinator of these seed ferns, whose pollen was too large for wind transport. Furthermore, some Upper Carboniferous plants produced glandular hairs that might have been an early type of nectary to attract pollinators (Scott and Taylor 1983).

Fossil data permit limited comparison of diversity and species interactions between taxonomically distinct fossil and extant communities (see also Chapter 9). Insect diversity has increased at a rate of about 1.5 families per 1 million years since the Devonian; the rise of angiosperms during the Cretaceous contributed to diversification within families but did not increase the rate of diversification at the family level (Labandeira and Sepkoski 1993).Arthropod diversity was high in the communities recorded in Upper Carboniferous coal deposits and in Dominican and Mexican ambers (Poinar 1993, Poinar and Poinar 1999, Scott and Taylor 1983). Similar associations, as discussed earlier in this section, indicate that virtually all types of interactions represented by extant communities (e.g., herbivore-plant, arthropod-fungus, predator-prey, pollinator, wood-borer, detri-tivore, etc.) were established as early as the Upper Carboniferous.

The behavioral fixity hypothesis permits reconstruction of prehistoric communities, to the extent that organisms associated in coal, amber, or other deposits represent prehistoric communities (e.g., Fig. 10.8) (Poinar 1993, Poinar and Poinar 1999). The Upper Carboniferous coal deposits indicate a diverse, tree ferndominated, swamp ecosystem. The fossils in Dominican amber indicate a tropical, evergreen, angiosperm rainforest. Some insect specimens indicate the presence of large buttress-based host trees, whereas other specimens indicate the presence of palms in forest openings (Poinar 1993, Poinar and Poinar 1999). The presence of fig wasps indicates that fig trees were present. Baltic amber contains a combination of warm temperate and subtropical groups, suggesting a number of possible community structures. The temperate elements could have originated at a higher elevation, or Baltic amber may have formed during a climate change from subtropical to temperate conditions (Poinar 1993). Diversity, food web structure, and functional group organization were similar between these extinct communities and extant communities (Poinar 1993, Scott and Taylor 1983), suggesting that broad patterns of community structure are conserved through time, even as species composition changes (Poinar and Poinar 1999).

The fossil record can record changes in community structure at a site through time. The degree to which particular community types are continuous across discontinuities in the strata at a site indicates consistency of environmental conditions and community structure (Boucot 1990, Labandeira et al. 2002). Boucot (1990) noted that, although a particular fossilized community (taxonomic association) rarely persists long in a local stratigraphic section, communities usually recur over larger areas for 106-107 years, indicating a high degree of stability within environmental constraints. Labandeira et al. (2002) compiled data for insect-plant associations spanning the Cretaceous-Tertiary boundary. They found

Species Insects
| Sciarid and phorid flies (Diptera) and spider from Columbian amber. From a sample containing >12 species of insects (4 orders) and spiders.

that specialized (monophagous) associations almost disappeared at the boundary and have not recovered to Cretaceous levels, whereas generalized (polyphagous) associations regained their Cretaceous abundances (Fig. 10.9). Wilf and Labandeira (1999) reported fossil evidence that insect herbivore diversity and intensity of herbivory increased during the global warming interval from the late Paleocene to early Eocene.

Pollen or other fossil records often indicate relatively rapid changes in distribution of particular plant species and, presumably, of associated heterotrophs. For example, Gear and Huntley (1991) reported that dating of fossilized Scots pine, Pinus sylvestris, stumps in northern Scotland indicated that pine forest expanded rapidly northward 70-80 km about 4000 years BP and persisted for about 400 years before retreating southward again, suggesting a 400-year period of warmer climate and community change. However, they noted that even this remarkably rapid rate of species movement would be insufficient (by an order of magnitude) to accomplish range change necessary for survival under future climate-change scenarios, especially if population spread were impeded by landscape fragmentation.

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