Ghosts of Competition Present
by Grant A. Mincy
There is a long held idea that ecological competition in the past is responsible for the species diversity and ecosystem structures we see today. This idea has been deemed the ghost of competition past. The ghost of competition present is an extension of the latter idea. The ghost of competition present hypothesis simply states that the effects of unsuccessful species on a final stable community have implications for that communities structure (Miller et al 2009). Simply put, unsuccessful invading species influence what species are successful in communities. There are four main ideas to the ghost of competition present idea:
- Successful species have weak interaction with other successful species.
- Successful species interact strongly with potential invading species.
- Successful species are influenced less by competition than their potential invaders (ghosts).
- When ghost species stop competing with an ecological community, species previously suppressed flourish, thus changing community composition (Miller et al 2009).
To help explain this idea, lets look at the long term effects of dinosaur extinction, and competition occurring today. The extinction of large dinosaurs allowed for the great diversification of both avian and mammalian faunas (Prothero 2004). Paleocene bird radiation, in fact, greatly resembles the mammalian diversification as the extinction of non-avian dinosaurs allowed for the evolution of large terrestrial vertebrates. The avian faunas at the time too experienced a grand radiation with the extinction of their closest relatives (Prothero 2004). The ghost of large terrestrial dinosaurs allowed for an onslaught of great diversification to the present day.
Moving from the Paleocene to the Holocene, mammalian radiation allowed for the establishment of human beings and the avian diversification allowed for the evolution of the Cerulean Warbler. Both species co-exist today and one can argue that they are currently competing for land and resources. In this scenario, humans are the ultimate invader. In some instances, such as strip mining, humans are restructuring ecosystems and habitat for the Cerulean Warbler in negative ways.
In terms of wilderness preservation though, humans are also contributing to the survival of the species. The Cerulean warbler is a charismatic song bird endemic to the Appalachian mountains. The Cerulean nests and raises its young in the Appalachian highlands among the canopies of deciduous trees. When not in the highlands, the songbird finds its home in mesic cove forests among large tracts of undisturbed habitat (USFWS 2006). Cerulean warblers nest and raise their young in large tracts of deciduous hardwood forests. For this reason they greatly enjoy the Cumberland Mountains in Tennessee because they remain mostly forested. They also prefer a large forest patch size and choose to nest in hickory, oak and maple trees (USFWS 2006). Cerulean’s are considered area-sensitive because they prefer breeding in large forest tracts. They will breed in smaller forested stands in areas where the larger landscape is well-forested (USFWS 2006).
The Warbler is an important species because it is experiencing a rapid population decline due to habitat depletion and fragmentation. 70% of the population has vanished in the past three decades because of anthropogenic land use (USFWS 2006). In terms of surface mining, MTR sites and permits awaiting authorization, are located within the key breeding zones of the Cerulean (Boves 2010). There have been multiple studies conducted and research initiatives implored to examine the plight of the Cerulean. What has been exposed about mining and the Cerulean is alarming.
Appalachia in general, along with the Cumberland mountains, have a large history of resource extraction, and this only continues to grow. In terms of surface mining in the region, the report states that Tennessee has 78.2 million tons of bituminous coal (Beachy 2008). Mining occurs in both northern and southern Tennessee, the mines affecting Warbler habitat in Northern Tennessee are MTR/cross ridge contour mining sites (Beachy 2008). MTR sites occur on steep ridges at high elevations in the Cumberland Mountains, coinciding with optimal habitat for the Cerulean (Beachy 2008). Currently, there are large gaps of forest and heavy fragmentation due to surface mines. There is also a very hard edge currently placed on Cerulean habitat (Beachy 2008). In regards to MTR, Cerulean’s still nest around reclaimed sites but the breeding success rate has steeply declined a and they have not responded well to the hard edge placed on their habitat (brood parasitism, hotter temperatures, etc). There is believed to be a dramatic loss of available Cerulean habitat in the coming years resulting in a continual decline in population throughout the Cumberland’s, a core breeding zone for the entire species (Bullock 2007).
There are anthropogenic influences, such as wilderness areas, national parks and national forests where Cerulean’s are still experiencing breeding success (Boves 2010). In these areas, the role of the invader is different. As opposed to habitat destruction for resource extraction, in these areas the invader looks to maintain ecosystem function. Here natural disturbances are mimicked, or in the case of fire are often mitigated to ensure ecosystem stability. In this setting, human beings are ghosts as they are not establishing dominance over a protected area.
In summary, competition in the Paleozoic, between large dinosaurs, suppressed mammal and avian evolution. Mammals were often prey and avian diversity was slowed because they later filled the niche space of a large predator. With the extinction of the dinosaurs, the great mammalian and avian radiation began. Mammal evolution allowed for human beings, and avian evolution allowed for the establishment of the Cerulean Warbler. Today, as ultimate invaders, human resource extraction, especially in regards to mountaintop removal coal mining, is causing a precipitous population decline to the Cerulean species because we are greatly altering their natural habitat. However, in ecosystems such as publicly protected lands, human beings are working to enhance ecosystem health while suppressing ecosystem disturbance. In this instance, human beings are acting as a ghost species, not establishing dominance over a system. For this reason, Cerulean’s are successful at breeding in non disturbed areas and, furthermore, biological diversity is much greater in these areas.