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Introduction
The uneven distribution of species is a key feature of life on Earth and has myriad implications. While the scale-dependance of determinants of the global variation in diversity is acknowledged [1-6], to date a quantitative accounting of the roles of history and environment in generating and maintaining gradients in species richness is still lacking.

Bioregion Biotic Independence
- expect stronger correlation of area and productivity integrated over time (Time-Area Productivity) with diversity of Endemic species

Bioregion Species Richness
- factors such as orbital forcing causing glaciation at high latitude have been posited to elevate extraction rates and expected to accentuate the observed disparities in species richness among bioregion, especially endemic one

Bioregion Biotic Independence
- expect stronger correlation of area and productivity integrated over time (Time-Area Productivity) with diversity of Endemic species

Bioregion Species Richness
- factors such as orbital forcing causing glaciation at high latitude have been posited to elevate extraction rates and expected to accentuate the observed disparities in species richness among bioregion, especially endemic one

Finer Scale Species Richness
- hypothesized that net primary productivity should be dominant predictor of fine grain assemblage richness

Using a few key predictor variables like time, area, productivity and temperature.

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Introduction
The uneven distribution of species diversity is a key feature of
life on Earth and has myriad implications. While the scale-
dependence of the determinants of the global variation in diversity
is well acknowledged [1–6], to date a quantitative accounting of
the roles of history and environment in generating and
maintaining gradients in species richness is still lacking.

Using just a few key predictor
variables—time, area, productivity, and temperature—we
are now able to explain more than 80% of the variability in
biodiversity among bioregions. By integrating each of
these factors at both the regional and local scale in a
hierarchical model, we are able to provide a consensus
explanation for broad-scale diversity gradients that en-
compasses both ecological and evolutionary mechanisms.

Global Gradients in Vertebrate Diversity primary productivity (Productivity) and Temperature.

Summed Productivity over bioregion Area yields total bioregion productivity
(AreaProductivity)—that is, total annual carbon flux measured in kg/
year over a whole bioregion, a measure that exhibits joint
dynamics with bioregion Area. But integrated over time in the form
of TimeAreaProductivity, it exhibits very different geographic patterns
than TimeArea (Figure 1) with, for example, African and IndoMalay
tropical moist forests experiencing a flux of over 8,00061017 kg of
carbon over the past 55 million years and the Mediterranean
regions of the New World and Africa just under 361017 kg.

Bioregion Biotic Independence
terrestrial vertebrate richness per bioregion as
Total (every species found in a bioregion), Resident (species for
which a given bioregion contains the largest portion of the range),
and Endemic (species that are restricted to a single bioregion; Table
S4). They find minimal overlap in Total species among bioregions
(median Jaccard similarity among bioregions: 4% for birds, 0% for
other taxa; Figure S1, Table S3), which confirms their relative
evolutionary isolation in addition to climatic and spatial
independence and a consistently strong pattern of biome
conservatism.

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Low number of species from basal birds clades in the extratrophs is confirmed by the global.
Worrld warmer and wetter in the late Cretaceous and early tertiary.
Climate change--> Latitudinal diversity.
Cooling and dry by spread and radiation --->newly cooler and drier habitat.
"Evolutionary time"(oligocene)
'the warm, wet throphic are richer because they have been climatically stable longer than the temperate zone.'

CLIMATE CHANGE HYPOTHESIS
-make this prediction because it argues that the elements of that influence diversity now are the same that have influence evolutionary time.
- the highest bird diversity is found warm. Wet climates both because bird diversity is found in warm, wet climate occupied longest.

Niche Conservatism will be shown to influence many groups, and it is also a fruitful approach to link ecological and evolutionary phenomena.

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1. Phylogenetic Analysis : phylogenetic analyses of the combined data for 325 and 140 taxa support the same major clades found by previous researchers.
2. Biogeographic Reconstruction : The analyses all agree that the ancestral area for Hylidae is tropical South America.
3. Ages of Clades : Major clades of tropical hylids appear to have split from each other before the expansion of the temperate regions.
4. Richness versus Time : Results show a very strong relationship between hylid species richness in a region and the time when that region was first colonized by hylids.
5. Latitudinal Variation in Diversification Rates : Nonphylogenetic analyses show that there is no relationship between the latitudinal midpoint of the clade and the absolute rate of diversification of that clade.
6. Ecological Niche Modeling : Analyses of ecological niche modeling for 6 species strongly suggest that temperate seasonality is the most important climatic variable that potentially limits the spread of 4 major hylid clades into temperate North America along the Gulf Coast of Mexico.

Phylogenetic Conservatism in a Climatic Niche Trait
- Analyses of mean species value for temperature seasonality suggest that tolerances of individual species for extreme seasonality are generally conserved across the phylogeny.
- This climatic niche variable is phylogenetically associated.

The result generally support the tropical hypothesis, but with 2 major caveats:
1. Temperature seasonality seems to limit the dispersal of tropical clades.
2. The study offer only a weak test of the role of the Cenozoic expansion of temperate regions in generating the latitudinal gradient.

Conclusion
a) The tropical conservatism hypothesis has been proposed as a general explanation for the latitudinal diversity gradient that links the ecological factors correlated with species richness patterns to the evolutionary and biogeographic processes.
b) In theory, the tropical conservatism hypothesis should apply to most groups of organisms with high tropical species richness. However, not every group will support its prediction.
c) The tropical conservatism hypothesis reflects the combined effects of two general factors:
- niche conservatism
- time-for-speciation effect

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[ Evolutionary and Ecological causes of the latitudinal Diversity of Hylid Frogs 

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[ Evolutionary and Ecological causes of the latitudinal Diversity of Hylid Frogs 

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1.Why are there more species in the tropics than the temperate region?
2. At least 100 hypothesis have been proposed to explain this pattern
(productivity,energy,stability hypothesis)
(Explicity or implicity hypothesis)
3.To fully explain species richness, we must know how ecological factor (climate) interact with evolutionary and biogeographic process.

3 Hypothesis (tropical conservatism hypothesis)
1st = group with high tropical species richness originated in the tropics and have dispersed to temperate region.
2nd = Dispersal of tropical grouos into temperate region is limited by their inability to adapt freezing
3rd = Large number of extant groups originated in the tropic until the temperate region expanded.

Why this research is important?

Because the 3 hypothesis has not been throughly tested in amy group of organism

Method use for this study
1. Phylogenetic analysis
2. Ascestral area reconstruction
3. Molecular dating analysis
4. Ecological niche modeling

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3 main hypotheses in historical time stability 

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3 main hypotheses in historical time stability 

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1. Historical Pertubation hypothesis is about low species richness of higher latitude Is a consequence Of an insufficient time period available for species to colonize or recolonise because of historical perturbation such as glaciation.
2. Evolutionary rate hypothesis is about higher evolutionary rates in tropic caused higher speculation rate. Some of the research done is about faster rates of microevolution in warm climates of plant, mammals and amphians.
3. Hypothesis Of effective evolutionary time is about the diversity is determined by evolutionary time where the ecosystem have existed and the evolutionary speed directly determined by effort of environment energy (temperature) on mutation rates, generation times and speed of selection.

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What is latitudinal gradients of Biodiversity?

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What is latitudinal gradients of Biodiversity?

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It is a biogeographic patterns that quantify the ways in which taxonomic, phylogenetic, functional, genetic or phenetic biodiversity change with latitudinal position on the surface of the Earth. Check out more in this short video guys!

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Biology Biodiversity & Conservation part 5 (Latitudinal Gradient) class 12 XII

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-More species in tropics
basal clades adapted to warm paleoclimates have been lost in regions now experiencing cool climates.
-Classify species as 'basal' and 'clades' based on their family -->molecular phylogenies are used so that richness pattern are identified.
BASAL CLADES- DIVERSE IN LOWLAND TROPICS
DERIVED CLADE- DIVERSE IN EXTRATROPICS AND HIGH ALTITUDE TROPICS

In studying birds, environmental variables are used to explain THE DIFFERENCES IN OLD AND NEW WORLDS.
In ecological time, the global richness gradients responses to climatic gradients. The gradients primarily reflects the extirpation ( local extinction) of species in older clades from parts of the world that have been cooler in the present.

"Path model"
basal-> rooted phylogenetic tree/cladogram direction of the base.
derived-> diverse and derived from the basal.
clade--> group of organism to compromise all the evolutionary descendants of a common ancestors.

old world/ Afro-Eurasia: west, refer to Africa, Europe, and Asia (Afro-Asia) *Aus and NZ are not included.
new world: Majority of Earth's western hemisphere, specifically the Americas. Including the Caribbean and Bermuda.

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- One of the hypothesis proposed in Latitudinal Diversity Gradient or LDG.
- Composed of :-
1) Abiotic Rarefaction
2) Ecological time
3) Evolutionary time

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[Global Gradients in Vertebrate Diversity Predicted by Historical Area- Productivity Dynamics and Contemporary Environment.]

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[Global Gradients in Vertebrate Diversity Predicted by Historical Area- Productivity Dynamics and Contemporary Environment.]

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This journal shows that a very conceptual to empirical explanation. We figured that how history can be integrated into a model predicting diversity with area, productivity and temperature at global scale. The first test of their pervasiveness at a global scale are the TimeAreaProductivity + Model. This model currently explains about 46%-60% and 32%-50% of the variation in resident richness and total richness. This finer scale affected by spatial scale and dispersal abilities. The hypotheses are net primary productivity should be a dominant predictor of richness. There are two reasons how the interval time works, which are the window of time and most ancestors vertebrate that dominate the diversity.