what causes latitudinal gradient

Full Answer

What is the latitudinal gradient in species diversity?

Latitudinal gradients in species diversity. Species richness, or biodiversity, increases from the poles to the tropics for a wide variety of terrestrial and marine organisms, often referred to as the latitudinal diversity gradient ( LDG). The LDG is one of the most widely recognized patterns in ecology.

Where does the latitudinal gradient occur?

Hillebrand found the latitudinal gradient occurs in marine, terrestrial, and freshwater ecosystems, in both hemispheres. The gradient is steeper and more pronounced in richer taxa (i.e. taxa with more species), larger organisms, in marine and terrestrial versus freshwater ecosystems, and at regional versus local scales.

Where do latitudinal gradients in Guild richness come from?

This indicates that latitudinal gradients in guild richness of communities primarily arise from latitudinal gradients in g-diversity (ie, regional species richness). These same approaches were used to assess latitudinal gradients of guild evenness, diversity, and dominance.

Does the mid-domain effect contribute to the latitudinal gradient?

Colwell and Lees (2000) called this stochastic phenomenon the mid-domain effect (MDE), presented several alternative analytical formulations for one-dimensional MDE (expanded by Connolly 2005), and suggested the hypothesis that MDE might contribute to the latitudinal gradient in species richness,...

What are 2 key factors in latitudinal gradients?

The two key factors in latitudinal gradients are evolutionary history and climate. Over the course of evolutionary time, species diversity may increase in a community as more speciation events occur. Tropical communities are generally older than temperate or polar communities.

What are the 3 factors that affect latitudinal gradient Class 12?

(i) Genetic diversity. (ii) Species diversity. (iii) Community and ecosystem diversity.

What is a latitudinal gradient?

A latitudinal biodiversity gradient (LBG) has been identified in almost all organisms that have been investigated, on land and in the sea. The gradient involves high species' numbers near the equator (at low latitudes) and lower numbers of species at high latitudes.

What is latitudinal gradient 12 biology?

What is latitudinal gradient? As we move from the equator to the poles, the biodiversity and species richness decreases. This is known as latitudinal gradient.

What are the two factors that determine the number of species on the island?

The number of species found on an island is determined by a balance between two factors: the immigration rate (of species new to the island) from other inhabited areas and the extinction rate (of species established on the island).

What are the causes of biodiversity loss class 12?

Causes for Loss of BiodiversityHabitat loss and fragmentation.Over-exploitation.Alien species invasions.Co-extinctions.

What are two key factors in species richness Equatorial polar gradients?

Two key factors in equatorial-polar gradients of species richness are probably evolutionary history and climate.

At which latitude there is maximum diversity class 12?

Species richness, or biodiversity, increases from the poles to the tropics. So the latitude range with maximum species diversity is the equator region, which is option C.

What is the latitudinal gradient?

Latitudinal gradients in species diversity. Species richness, or biodiversity, increases from the poles to the tropics for a wide variety of terrestrial and marine organisms, often referred to as the latitudinal diversity gradient ( LDG ). The LDG is one of the most widely recognized patterns in ecology.

Why is the latitudinal diversity gradient?

Similarly to the climate harshness hypothesis, climate stability is suggested to be the reason for the latitudinal diversity gradient. The mechanism for this hypothesis is that while a fluctuating environment may increase the extinction rate or preclude specialization, a constant environment can allow species to specialize on predictable resources, allowing them to have narrower niches and facilitating speciation. The fact that temperate regions are more variable both seasonally and over geological timescales (discussed in more detail below) suggests that temperate regions are thus expected to have less species diversity than the tropics.

How many hypotheses are there for the latitudinal diversity gradient?

Although many of the hypotheses exploring the latitudinal diversity gradient are closely related and interdependent, most of the major hypotheses can be split into three general hypotheses.

What is LDG pattern?

The LDG is one of the most widely recognized patterns in ecology. The LDG has been observed to varying degrees in Earth's past. A parallel trend has been found with elevation ( elevational diversity gradient ), though this is less well-studied.

How is evolutionary time determined?

The hypothesis of effective evolutionary time assumes that diversity is determined by the evolutionary time under which ecosystems have existed under relatively unchanged conditions , and by evolutionary speed directly determined by effects of environmental energy (temperature) on mutation rates, generation times, and speed of selection (Rohde 1992). It differs from most other hypotheses in not postulating an upper limit to species richness set by various abiotic and biotic factors, i.e., it is a nonequilibrium hypothesis assuming a largely non-saturated niche space. It does accept that many other factors may play a role in causing latitudinal gradients in species richness as well. The hypothesis is supported by much recent evidence, in particular, the studies of Allen et al. (2006) and Wright et al. (2006).

How does area affect biodiversity?

The effect of area on biodiversity patterns has been shown to be scale-dependent , having the strongest effect among species with small geographical ranges compared to those species with large ranges who are affected more so by other factors such as the mid-domain and/or temperature.

Why are extinction rates reduced towards the equator?

Put another way, this hypothesis suggests that extinction rates are reduced towards the equator as a result of the higher populations sustainable by the greater amount of available energy in the tropics. Lower extinction rates lead to more species in the tropics.

What are latitudinal gradients?

Latitudinal gradients of biodiversity are biogeographic patterns that define the ways in which components of taxonomic, phy- logenetic, functional, genetic, or phenetic biodiversity change with latitudinal position on the surface of the earth.

What is the latitudinal gradient in which richness peaks in the tropics?

The latitudinal gradient in which richness peaks in the tropics may be a consequence of the larger landmass of the tropics compared to other geographic zones. This simple idea had its genesis in the work of Terborgh (1973), with considerable development and refinement by Rosenzweig (1995), who incorporated the effects of productivity and zonal bleeding into a more comprehensive conceptual model. Nonetheless, the geographic area hypothesis has generated considerable controversy and contention (Rohde, 1997, 1998; Rosenzweig and Sandlin, 1997). The controversy does not surround whether an areal mechanism operates; rather, it focuses on the degree to which variation in area is the dominant factor molding latitudinal gradients in richness. Two features of the earth’s geometry predispose the sizes of tropical regions to be greater than those of their higher latitude counterparts. First, the earth is essentially a sphere. The distance between longitudinal meridians at the equator is greater than that elsewhere on the globe, and inter-meridian distance decreases in a regular fashion toward the poles. Second, northern and southern tropical zones are adjacent, whereas the northern and southern variants of other latitudinally defined zones are isolated from each other. Nonetheless, the positions, sizes, and configurations of the earth’s continents will affect the proportion of land or water at each latitude, and this has varied over geological time as a consequence of plate tectonics. In addition, the number and breadth of zones used to subdivide latitude will affect the perception of areal dominance associated with the tropics. For example, a tripartite division (tropical, temperate, and polar) of terrestrial environments reveals that the tropics rank second in area to northern temperate regions at the global scale, with considerable variation in the proportional area represented by the tropics among continents (approximately 38, 12, 80, 41, and 0% of America, Eurasia, Africa, Australia, and Antarctica, respectively). In contrast, finer resolution of terrestrial zones to tropical, subtropical, temperate, boreal, and tundra indicates the areal pre- dominance of tropical lands globally. Most important, the degree of environmental variation within the tropics is less than that in other geographic zones, at least with respect to incident solar radiation and temperature. Specifically, a band of 50 degrees centered on the equator evinces no or little change in mean annual temperature with latitude (constant at approximately 271C), whereas mean annual temperature

What is the grand proliferation of hypotheses?

A grand proliferation of hypotheses (Table 1), along with subsequent a posteriori modifications, characterizes the latitudinal gradient literature. Each hypothesis represents a conceptual model with only qualitative predictions. As with much of macro- ecological research, broad-scale data concerning the distribution of species is not available for many taxa. Manipulative experi- ments designed to disentangle the effects of competing hypotheses are not feasible or ethical. In addition, the inherent geographic factors that might affect richness are often correlated so that efforts to remove the effect of one to assess the other can lead to spurious results due to the confounded nature of the mechanisms. Indeed, most of the hypotheses represent conceptual models that lend insight into how nature could operate and provide only a general qualitative prediction that richness should increase toward the tropics, but do not generate unique predictions based on direct features of the gradient that conclusively refute any of the competing hypotheses. Moreover, many hypotheses are circular in nature and the indirect predictions that they make about latitudinal gradients have not been examined comprehensively from an empirical perspective. In addition, some hypotheses only pertain to particular taxa or ecological groups, so that they are not applicable universally. Rather than elucidating the score of extant hypotheses, which has been done to greater or lesser extents elsewhere (Rohde, 1992; Rosenzweig, 1995; Gaston, 1996), an exposition of selected hypotheses that have generated considerable debate in the literature follows.

What are the latitudinal gradients of biodiversity?

Latitudinal Gradients of Biodiversity 3. Latitudinal gradients in other aspects of taxonomic biodiversity (eg, species or generic evenness, diversity, dominance, and rarity) as well as in other dimensions of biodiversity (eg, functional, phenetic, and phylogenetic) have received increasing attention during the past decade.

How is latitudinal variation related to biodiversity?

The ways in which latitudinal variation in biodiversity at broad spatial scales (ie, g-scale) is related to patterns of biodiversity at the level of local communities (ie, a-scale) is unclear. In part, this is because the geographic boundaries of a community are difficult to designate and are ultimately arbitrary decisions. Moreover, until recently, little was known about the composition of local communities in tropical regions, making assessment of broad-scale latitudinal patterns of biodiversity a premature endeavor at the community level. Finally, it is unlikely that a single research scientist can gather sufficient data across many sites to assess latitudinal gradients in biodiversity with sufficient power to distinguish ecological patterns from random variation. Hence, compositional data must be compiled from the work of many different individuals, who often use different methods, designs, and sampling intensities, to quantify the gradient in a meaningful way. Concern regarding adequate sampling within a community (eg, Voss and Emmons, 1996) must be tempered by the realization that community composition has a temporal dynamic. Communities represent suites of populations with the potential to interact, and thus must be constrained to some extent by both time and space. Sampling regimes that extend over protracted periods of time (eg, decades or longer) may have inflated estimates of richness and inaccurate assessments of species composition. Nonetheless, recent progress in this regard allows quantitative evaluation of patterns in a rigorous way, at least for some taxonomic groups. When care is taken so that a local community is delimited as a geographic area in which constituent species have a high likelihood of co-occurrence in space and time, it is clear that species richness increases from polar through temperate to tropical regions. For example, data for bats from 32 local communities (Stevens and Willig, 2002) that met rigorous standards for Table 1 Mechanisms potentially affecting the latitudinal gradient in species richness Circular Empirically unsubstantiated Competition Environmental stability Mutualism Environmental predictability (contingency) Predation Productivity Epidemics Abiotic rarefaction Biotic spatial heterogeneity Physical heterogeneity Population size Angle of the sun above the horizon Niche width Area Population growth rate Aridity Patchiness Seasonality Epiphyte load Number of habitats Host diversity Rapoport’s rule (range size gradient) Harshness Ecological time Evolutionary time Temperature dependence of chemical reactions Solar energy Evolutionary speed Stochastic placement of species ranges

What is the species richness of regions, biomes, or climatic zones?

In part, the species richness of regions, biomes, or climatic zones is a consequence of the species richness that occurs in constituent local communities. Similarly, the species richness and composition of local communities are affected by the set of taxa that constitute regional species pools (Putman, 1994).

What is gradient in biology?

In the context of this article, a gradient implies a gradual change in biodiversity with a gradual change in latitude. In an unambiguous fashion, the form of that pattern is the precise mathematical or statistical relationship that describes how biodiversity changes with latitude. As a consequence, three considerations are important in assessing patterns: the general shape of the curve (eg, symmetry, kurtosis, or linearity), the parameters that characterize the relationship, and the degree to which the fit of empirical data to the predicted curve is equivalent to the north and south of the equator. Knowledge of these three aspects of gradients suggests the kinds of causal mechanisms that are in operation. In addition, it facilitates comparison of gradients among taxa within the same geographic domain (Fig. 1; birds, mammals, reptiles, and amphibians in North America) as well as comparisons among different geographic domains for the same taxon (Fig. 4; North American and South American for mammalian orders). Patterns are often scale dependent, with particular mechanisms having larger effects at some spatial scales than at others. Consequently, patterns can be evaluated at a variety of scale, ranging from biotic assemblages that occupy large areas (eg, biogeographic regions, biomes, or climatic zones) to ecological communities occupying local sites. These scales are intimately associated with each other. In part, the species richness of regions, biomes, or climatic zones is a consequence of the species richness that occurs in constituent local communities. Similarly, the species richness and composition of local communities are affected by the set of taxa that constitute regional species pools (Putman, 1994).

Overview

Patterns in the past

Hypotheses for pattern

Synthesis and conclusions

See also