I. A Competitive Edge
The best races have the best competitors, and angiosperms have certainly been described as having an extra edge. As discussed in the introduction, the fossil record shows that gymnosperms were quickly displaced by angiosperms upon their arrival. Yet despite the number of hypotheses (table 1) put forward to explain this shift in vegetation, gymnosperms’ competitors have not yet been discovered.
Among the numerous hypotheses, three are discussed in depth here (summarised in fig. 1). The first two hypotheses are largely centred around Bond’s (1989) slow seedling hypothesis (Box 1), which induced an assortment of literature surrounding the topic. The final hypothesis discusses the ecological advantages that are thought to …show more content…
In such conditions, there is usually an unlimited supply of nutrients, light and water; thus, optimal growth is recorded, rather than effective growth (which may be much lower). In fact, surveys of mature trees in natural field conditions have found that not only can the transport capabilities of gymnosperms and angiosperms be quite similar (Becker, 2000), but also that conifers and angiosperms may have similar growth rates (Reich, Grigal, Aber, & Gower, 1997). Coniferous forests can even have higher growth rates than their angiosperm counterparts in comparable regions (Downing & Weber, …show more content…
In accordance with Bond (1989), gymnosperm restriction to low productivity areas hinges on the idea that they have less efficient water vascular systems. Thus, they were excluded from regeneration niches ‘by default’. Pitterman et al. (2012) find support for this idea, reporting that ancient cypress conifers were not drought tolerant; tolerant clades only appeared after the Eocene. Despite this, conifers (at least, modern conifers) have higher drought resistance than angiosperms, able to survive even in severe drought conditions (Augusto, Davies, Delzon, & De Schrijver, 2014). Consequently, the advent of dry niches may explain the initial rise of the angiosperms, but cannot describe a competitive edge throughout all time periods.
Hypothesis 3: Ecological Innovation of the Angiosperm
Because abiotic factors often limit angiosperm dominance (Bond, 1989), an intuitive idea is that acquisition of ecological innovations (in terms of biotic interactions) have allowed for supreme angiosperm competition. Three further hypotheses are often outlined in the literature, concentrating on herbivory, reproduction and symbioses.
The best races have the best competitors, and angiosperms have certainly been described as having an extra edge. As discussed in the introduction, the fossil record shows that gymnosperms were quickly displaced by angiosperms upon their arrival. Yet despite the number of hypotheses (table 1) put forward to explain this shift in vegetation, gymnosperms’ competitors have not yet been discovered.
Among the numerous hypotheses, three are discussed in depth here (summarised in fig. 1). The first two hypotheses are largely centred around Bond’s (1989) slow seedling hypothesis (Box 1), which induced an assortment of literature surrounding the topic. The final hypothesis discusses the ecological advantages that are thought to …show more content…
In such conditions, there is usually an unlimited supply of nutrients, light and water; thus, optimal growth is recorded, rather than effective growth (which may be much lower). In fact, surveys of mature trees in natural field conditions have found that not only can the transport capabilities of gymnosperms and angiosperms be quite similar (Becker, 2000), but also that conifers and angiosperms may have similar growth rates (Reich, Grigal, Aber, & Gower, 1997). Coniferous forests can even have higher growth rates than their angiosperm counterparts in comparable regions (Downing & Weber, …show more content…
In accordance with Bond (1989), gymnosperm restriction to low productivity areas hinges on the idea that they have less efficient water vascular systems. Thus, they were excluded from regeneration niches ‘by default’. Pitterman et al. (2012) find support for this idea, reporting that ancient cypress conifers were not drought tolerant; tolerant clades only appeared after the Eocene. Despite this, conifers (at least, modern conifers) have higher drought resistance than angiosperms, able to survive even in severe drought conditions (Augusto, Davies, Delzon, & De Schrijver, 2014). Consequently, the advent of dry niches may explain the initial rise of the angiosperms, but cannot describe a competitive edge throughout all time periods.
Hypothesis 3: Ecological Innovation of the Angiosperm
Because abiotic factors often limit angiosperm dominance (Bond, 1989), an intuitive idea is that acquisition of ecological innovations (in terms of biotic interactions) have allowed for supreme angiosperm competition. Three further hypotheses are often outlined in the literature, concentrating on herbivory, reproduction and symbioses.