Ecology

Answer:

Savanna biomes have two distinct seasons; winter and summer. These seasons are however, accompanied by the extreme rise and fall in temperature associated with these seasonal distinctions. The rainy season in the biome occurs during the summer season while the winter remains dry.
The topical dry forests are generally warm all round the year. There are alternating dry and wet seasons. Dry seasons last longer, while the rainy season is shorter than the dry season.
The seasonality in the rainfall of these two biomes is caused due to the shifts in the latitude at which the sun is directly overhead. As the earth revolves around the sun, this shift in the latitude occurs approximately between 23.5°N and 23.5°S. This shift in the latitudes is responsible for the generation of tropical storms.
In the tropical Savanna and the tropical dry forest biomes, the wet season occurs during the warm months of the year, which is the time during which the sun is almost overhead in these regions.

Answer:

Daniel Jansen's study of the guanacaste tree led him to the conclusion that the dispersion of the seeds of the tree was carried out by the large herbivorous animals including ground sloths, camels and horses following the end of Pleistocene about 10000 years ago. However, these animals became extinct probably due to over hunting by humans.
As a result, for thousands of years, the seeds produced by the guanacaste tree were not dispersed effectively in the absence of the dispersers. However, it continued to produce a large number of fruits. This led to the significant reduction in the number of Guanacaste trees in the region.
There would have been numerous other plants which were dependant on these large herbivorous animals for the dispersal of their seeds. After the extinction of these animal species, these trees too would have suffered low dispersal leading to an adverse effect on the plant population size. Some of them may also have got extinct.
However, many of these plant species survived, like the guanacaste tree. This fact suggests that some alternative mechanisms of seed dispersal may have existed or alternative dispersers may have done the job of seed dispersal for these trees.
Alternative means of the seed dispersal could be through multiple different vectors such as rodents and the other small animals. Also, the plants would have had to depend more on abiotic factors such as wind and rain for seed dispersal. Some trees are known to have evolved special structures on their fruits. Some examples of such structures are long and curved outgrowths which can easily cling on to animal feet and body parts. Hence, they get dispersed with the moving animals.