9,500,000 years ago: Our team has returned and noticed the impact of Global climate cooling on this region of Kalimor. The drop in rainfall and changes to the seasons has seen a change in the distribution of the Zebra populations. Expansion of grassland has seen an increase in the overall Zebra population.(See figure 3.4) We have noticed changes in both the timing and location of migration patterns. The Kallipo Zebra's population is increasingly migrating to newly opened Eastern grasslands rather than the western grasslands. The Delta population are starting their migrations later and spending less time on the grasslands. This has decreased gene flow between these population groups and we are starting to notice some variation in coat coloring and physical size. These differences are not clear enough for us to be able to classify them as different subspecies. Gene flow has been diminished, but is clearly still occurring producing a range of hybrids which makes classification difficult.

Climatic cooling and over grazing has also lead to changes in the species of grasses growing in the Western Grasslands. Analysis of grass species is showing an increase in silica content. High silica content makes the grass less palatable to herbivore species and discourages soft toothed browsers. Over grazing and climate change has increased the rate of grass evolution which in turn has affected zebra evolution. Comparisons of skulls from both populations (see figures 3.1 and 3.2) show some minor variation in incisor size and molar thickness. This is an example of co-evolution.

8,000,000 years ago: Our team has returned and the planet is undergoing a major period of Global Warming. Rising temperatures has lead to an increase in evaporation and rainfall in Central Kalimor. Savanna and deciduous forest have started to encroach on the grassland. But large populations of Elephants in Eastern Kalimor are preserving the available grassland around rivers and lakes. There is clear variation in the two major populations of Zebra and we are now classifying them as sub-species.

Equus burchelli plainus is also exhibiting clear morphological changes in its skull including a larger jaw bone and with increased incisor and molar teeth size. We are also seeing variation in strip pattern compared to Equus burchelli plainus with a an extra strip becoming more common in the population.

The isolated pockets of grassland mean that populations are no longer mixing during the mating season which has stopped gene flow between these two populations.

6,000,000 years ago

Equus burchelli planius: The collision between the continent of Darkland and Kalimor has seen the rapid increase in mountain uplift and the pushing up of plateau to the east of the Dragma mountain chain. The change in altitude in central Kalimor leads to dramatic climatic changes. The cooling climate has lead to the dominance of high silica grass. Many herbivores lack teeth that grow through out their lives. The climate change selected against these herbivores and in particular lead to the extinct of a number of gazelle species and the extinction of the wildebeest. Within the Zebra population there as variation in tooth growth patterns and larger incisors and molar were selected for.The drop in other herbivores lead to a increase in predation by the larger carnivores on the Zebra herds in this region. Lack of resources and increased competition favored more generalist hunters like hyenas and Leopards. The population size of Lions in particular dropped as their dominant source of food was Zebra and Wildebeest. This causes a bottleneck effect in the Equus burchelli plainus population. The decrease in Zebra population along with the arrival of new predator species from the continent of Darkland (Darkland tiger and Wild Dog) will have a major impact on Zebra evolution in this region.

Equus burchelli kallipo: Global warming has lead to the expansion of deciduous forest and the lose of grassland habitat. Elephants still play an important role in clearing trees to promote grass growth. Population sizes seem smaller and cluster around rivers and lakes in this region. The major changes are a darkening of the coat and a decrease in size.

4,000,000 years ago

Equus burchelli planius: We notice a change in the dominant predators in central Kalimor. The Darkland Tiger has replaced the lion, but mainly hunts larger herbivores like Elephants. The wild dog and Hyenas are now the dominant predators of Zebra in this region of Kalimor. We have observed changes in the kinship group structure. The size of kinship groups increases to an average of 10 mares and two mating males. More aggressive defensive behavior has started to appear in the population. Larger kinship groups and bachelor male groups now aggressively defend their foals from these predators. The forming of alliances between breeding males is of particular interest. Climatic cooling along with smaller predators has favored larger zebra with thicker layers of fat and fur. Zebra kinship groups are now spending all year on central grassland plateau and the migration of herds to the coast has stopped. A less variable climate, easy access to water and Larger kinship groups have contributed to the abandonment of migration. Natural selection would have favored individuals that didn't expend excess energy on the seasonal migration.

Equus burchelli kallipo: Sea level rise and increased rainfall sees a rapid decrease in grassland on Eastern Kalimor. Deciduous forest have replaced most of the grassland. This has caused a large drop in the Equus burchelli kallipo population. They no longer migrate and spend most of their time in small kinship groups feeding next to lakes and rivers in the forest. Mating season is not restricted to the rainy season. Zebra are smaller in size to move easily through the dense forest under story. Their coat has darken to blend into the shadow of the forest. Their major predator is the leopard and their sense of hearing has improved leading to a slightly larger ear. Darkland tigers have arrived in the region and have lead to a drop in the Elephant population.

2,000,000 years ago

Our team returns to find that the Equus kalmore species of Zebra appears to have gone extinct. The loss of grassland due to removal of the keystone species, Elephant and increased predation by Leopard seems to be the dominant reasons for this extinct.

The interior plateau is home to the thriving population of Equus planius.

Present:

The Eastern species of Zebra, Equus kalmore is extinct. Equus planius still survives on the central Kaloree plateau. Although population size appears to be lower than on our previous visit.

Figure 3.4: Phylogenic Tree of Zebra Evolution

Part 2: Speciation Event:

Clearly a speciation event has occurred since out last visit. (See figure 3.4) Our team has concluded that this is an example of sympatric speciation. Gene flow between the two populations slowly diminished over time during to changes in grassland location and mating seasons. Zebra's only mate in the two month period after giving birth. Since the Zebra's give birth on the grasslands after the start of the rainy season, mating occurs on the open grassland. Originally the two populations mixed during mating season on the central grasslands leading to gene flow between the populations. Once grasslands opened to the east and the two major populations started migrating to different regions, they no longer mated together. Over time changes seasonal rainfall patterns and the almost year round availability of water on the eastern grasslands lead to changes in migrations times and mating seasons between the two populations.(see figure 3.5)

Figure 3.5: Changes in mating times

This acted as the initial reproductive isolating mechanism. Behavioral changes would then be the isolation mechanism if the populations ever came together again. Although hybrids must have formed at times, natural selection would have not favored them because the mixed signals in mating times and behaviors would have made it difficult for hybrids to select mates.

Figure 3.6: Equus burchelli

Figure 3.7: Equus plainus

Figure 3.8: Equus kaloree

Part 3: Equus planius: (See figure 3.7)

Habitat: This species is located on the central Kaloree plateau. The average elevation is 4500m. At this high elevation the dominant biome is grassland and riparian. Average temperatures are lower than normal grassland. It is home to a number of herbivore species in including mountain sheep and goats and is dominated by pack hunting predators like the Hyena and Wilddog. Water is plentiful, but winter snows can cover much of the ground during the bitter winters.

Physical Adaptations: Equus planius is larger than the original introduced species, Equus burchelli. The open terrain, high elevation and thinner air favored individuals in the population with a greater lung capacity. This is evident in the larger chest dimensions we have observed. Longer leg length and increased muscle mass was selected for with the increased predation by packing hunting predators. The lighter coat color helps them blend into the often snow covered rocky terrain. The increase in size decreases the surface area to volume ratio. Combined with a thicker fat layer and a thicker winter coat which is shed suring summer allows this species to survive the harsh winters. We believe the distinctive mane found on males is an example of sexual selection.

Diet and feeding patterns: The evolution of high silica grasses lead to clear changes in teeth and skull size. (see figures 3.1 and 3.2) Increase in incisor size and molar thickness has required larger masticatory muscles. Measurements of jaw bones show a clear increase in size compared to other species of Zebra on Arda. Population migrate into the valleys that drain the plateau during winter, but spends spring and summer on the high plateau.

Behavior and Social Organization: The development of the larger complex kinship group structure is directly linked to the change in predation. The removal of large predators and the dominance of pack hunting predators like Hyena and Wild dogs favored increased cooperation between males. Pack predators rarely kill large adult Zebra and tend to try to run down the young and sick. The increase in the physical size of the zebra and larger kinship groups was favored by natural selection.

Courtship and Reproduction: The harsher climate has led to a rise in the age of ovulation from 1 year to 3 years old. Mothers still suckle their young up to 16 months, but no longer come into Estrous 2 months after birth. Estrous is now postponed till 14 months after birth allowing kinship groups to better protect the young. The average juvenile mortality has dropped from 50% to about 25%. This drop in mortality rate is balanced by the decrease in birth rate keeping the population size relativity stable.

Part 4: Equus kaloree: (See figure 3.8)

- Then write a summary of the evolution of your organism in four parts.