Catherine L. Cardelús

Global Warming, Elevational Range Shifts, and Lowland Biotic Attrition in the Wet Tropics

Many studies suggest that global warming is driving species ranges poleward and toward higher elevations at temperate latitudes, but evidence for range shifts is scarce for the tropics, where the shallow latitudinal temperature gradient makes upslope shifts more likely than poleward shifts. Based on new data for plants and insects on an elevational transect in Costa Rica, we assess the potential for lowland biotic attrition, range-shift gaps, and mountaintop extinctions under projected warming. We conclude that tropical lowland biotas may face a level of net lowland biotic attrition without parallel at higher latitudes (where range shifts may be compensated for by species from lower latitudes) and that a high proportion of tropical species soon faces gaps between current and projected elevational ranges.

Ferns in an Angiosperm World: Cretaceous Radiation into the Epiphytic Niche and Diversification on the Forest Floor

The Cretaceous period saw dramatic shifts in the functional plant biology of the Earth’s flora. This was an episode of explosive plant radiations that produced our modern angiosperm-dominated world. This period was also a time of great Pteridophytic diversification and experimentation and saw the rise of most extant fern lineages. Prominent among these was the widespread appearance of epiphytic species. In modern tropical forest canopies, epiphytic ferns often represent some of the most abundant taxa and can dominate epiphyte biomass. Yet from most perspectives, the epiphytic habitat is vastly different from the forest floor. What happened during the Cretaceous that led to such widespread epiphyte fern diversification? What are the traits that allow extant ferns to flourish in this dry, nutrient-poor, bright habitat? How did terrestrial ferns cope with this new habitat? We review a number of functional aspects of fern biology to include both gametophytic and sporophytic physiology. It is possible that angiosperms engineered conditions that lead to aseasonal tropical forests. Data suggest that ferns may have reduced water use efficiency. If so, then wetter forests may have facilitated fern diversification. Successful epiphytic species would have required major modification in the gametophyte generation to include indeterminate growth, extreme stress tolerance, and an outcrossing breeding system. Terrestrial species also radiated at this time and may have relied on unique aspects of photobiology to take advantage of low-light terrestrial habitats. The study of fern ecology has reached a fevered pitch. Continued investigation will no doubt reveal some of the most exciting changes in our understanding of this remarkable lineage.

Habitat differentiation of ferns in a lowland tropical rain forest.

Abstract Fern species and growth form diversity peak in tropical rainforests. In such forests, ferns often play important ecological roles. However the distribution and diversity patterns of different growth forms (i.e., epiphytic vs. terrestrial ferns) have not been broadly quantified. We compared the distribution and diversity patterns of epiphytic pteridophytes on the trunks of six individuals of the emergent canopy tree species Hyeronima alchorneoides (Euphorbiaceae) to those of terrestrial species at La Selva Biological Station in Heredia province, Costa Rica. A total of 21 species of epiphytic and 20 terrestrial ferns was recorded, with only one species found as an epiphyte and as a terrestrial species. Epiphytic species also exhibited increasing species diversity with increasing trunk height. Epiphytic species exhibited predictable patterns of distribution along the trunk and were easily grouped into high-trunk, low trunk, or bimodal categories. In terms of percent cover and number of species, simple-leaved ferns dominated the epiphytic growth form, 13 of 21 species, whereas ferns with compound or dissected leaves dominated the hemi-epiphytic and terrestrial floras with 20 of 20 species. These results indicate that there are significant functional differences in the ecology of epiphytic and terrestrial ferns and that reciprocal establishment is difficult and extremely rare.

Ants mediate nitrogen relations of an epiphytic fern

Henry David Thoreau once said that ‘nature made ferns for pure leaves to show what she could do in that line’ (Myerson, 1992). Indeed, ferns have thoroughly explored the diversity of leaf function and use the laminar surface as a site for both carbon fixation and reproduction. The fern’s lack of flowers has led most to overlook the potential for fern–animal interactions. Yet recent discoveries of lepidopteron soral crypsis in several tropical ferns (Barker et al., 2005) combined with an increased understanding of fern–herbivore interactions (Balick et al., 1978; Auerbach & Hendrix, 1980; Weintraub et al., 1995; Jensen & Holman, 2000; Mehltreter et al., 2003), and the presence of myrmecotrophy in some species (Rashbrook et al., 1992), demonstrate that fern–animal interactions may be more common than once thought. Myrmecotrophy is an intriguing and important plant–animal relationship that has significant consequences for plant nutrition, protection, and ecosystem-level processes (Solano & Dejean, 2004; Fiedler et al., 2007; Palmer & Brody, 2007; Sternberg et al., 2007). In the myrmecophytic relationship, host plants typically provide food resources, for example elaiosomes, extrafloral nectaries (Beattie, 1989), and/or suitable nesting spaces (myrmecodomatia) for the ant visitor. In return, it is assumed that ants protect their host plants by removing herbivores and pathogens, attacking competing vegetation (Janzen, 1969) and supplying nutrients (Kaufmann & Maschwitz, 2006). Myrmecotrophy has been reported in ferns, and species of Solanopteris (Forel, 1904; Gómez, 1974, 1977), Lecanopteris (Gay, 1991, 1993b; Gay & Hensen, 1992), and Polypodium (Koptur et al., 1998) are known to produce potato-like tubers that function as domatia. Limited evidence suggests that nesting ants act to protect host ferns as in the case of Solanopteris brunei, where Azteca ants become quite aggressive when their host plant is disturbed (Gómez, 1974; and personal observation). Perhaps one of the best known temperate fern–ant relationships occurs in the widespread bracken fern (Pteridium aquilinum). This species produces foliar nectaries, and several studies have examined the ecology of this phenomenon, finding limited to no influence of ants on the host plant and vice versa (Tempel, 1983; Heads & Lawton, 1984; Lawton & Heads, 1984; Heads, 1986; Rashbrook et al., 1992). Such results have added to the general rejection of the importance of fern–ant relationships. Apart from serving as a protective mechanism, ants may also contribute to host plant nutrition. While there are a large number of papers dealing with ant gardens and host plant interactions (Kaufmann & Maschwitz, 2006), quantification of nutrient exchange between ants and their plant host in natural conditions has not been widely demonstrated in epiphytic taxa and less so in ferns. Gay (1993a) conducted an elegant series of labeled nitrogen (N) laboratory experiments clearly demonstrating nutrient exchange between ants and host plants in the fern genus Lecanopteris. In this study, ant-derived nutrients were taken up through the inner walls of the domatia and, in at least one species, via roots produced inside such domatia. While Gay (1993a) demonstrated uptake, the study did not demonstrate the relative importance of this relationship to the overall nutrient budget of the host plant. In another example of N exchange in a myrmecophytic epiphyte, Treseder et al. (1995) demonstrated that the Asclepiad Dischidia major (Vahl) Merr. may derive up to 39% of its carbon and 29% of its N budget from ants that it hosts in specialized domatia (Treseder et al., 1995). Here we describe a previously unknown cryptic relationship between the fern Antrophyum lanceolatum and the ant Pheidole flavens and comment on its ecological significance.

Uniting church and science for conservation.

Humans have been cutting Ethiopian forests for fuel and agriculture for centuries ([ 1 ][1]). Only about 35,000 fragments remain in the northern highlands, ranging in size from 3 to 300 hectares. These fragments escaped deforestation because of their religious and spiritual importance; they are

Add ecology to the pre-medical curriculum.

In their Letter “Competencies: A cure for pre-med curriculum” (11 November 2011, p. [760][1]), W. A. Anderson and colleagues endorse a proposed shift in pre-medical education toward core competencies. We believe that the specific competencies proposed by the Association of American Medical

Church Forest Status and Carbon Sequestration in Northern Ethiopia

Ethiopia boasts one of tropical Africa’s richest biodiversity, predominantly in her forest fragments (Tolera et al. 2008). However, forests in northern Ethiopia have undergone severe deforestation, with an estimated 4% remaining (Gatzweiler 2007; Wassie et al. 2009). Human activities ranging from subsistence agriculture to collecting firewood are causal factors in a country where population has nearly doubled in 20 years from 43 million in 1984 to almost 80 million by 2000 (Feoli et al. 2002). The last remaining forest fragments in northern highlands of Ethiopian (called the Amhara Region) are housed in some 35,000 forest fragments called “church forests” that range from 3 to 300ha in size and date back 1500 years. Protected by the Orthodox Tewahido Church (EOTC, Wassie 2002), these fragments represent spiritual as well as biodiversity sanctuaries of both flora (Bongers et al. 2006; Wassie and Teketay 2006) and fauna (Lowman 2010a). For example, some plants species are found only within a few fragments (Wassie 2002). The church leadership view biodiversity conservation as one of its primary stewardships, but the lack of perimeter delineation of these forest fragments threatens their future.

Fertilization influences the nutrient acquisition strategy of a nomadic vine in a lowland tropical forest understory

AimsTropical tree and lianas in the understory are limited by soil nutrients despite growing in extremely low light. It is not known if nomadic vines are also limited by nutrients in low light conditions.MethodsWe measured differences in root architecture and mycorrhizal colonization, and leaf nutrients of a nomadic vine, Philodendron fragrantissimum (Araceae), in nitrogen (N) and phosphorus (P) fertilization plots in a lowland tropical moist forest in central Panama to measure potential nutrient limitation.ResultsRelative to plants in control plots, leaf P concentration was 54% higher and leaf N concentration was 10% higher for plants in the P- and N-addition treatments, respectively. The N:P of leaves suggested P-limitation in the N-addition treatment and the control but not in the P-addition treatment. Root branching was highest in the P-addition treatment, and P-addition reduced mycorrhizal colonization.ConclusionsThe large effect of P fertilization suggests that, like many tropical plants, P. fragrantissimum has the potential to be P-limited. Although further study is needed, we suggest that nomadic vines be added to the growth forms that respond to nutrient addition in the forest understory and conclude that nutrient-limitation seems like the rule rather than the exception in the light-limited understory.