Explanation:

Species are expected to shift towards poles: This statement is correct. One of the observed and predicted effects of global warming is the shift of species ranges toward the poles. As global temperatures rise, many species, particularly those unable to adapt rapidly, are moving towards higher latitudes (closer to the poles) where the environment is cooler. This is true for various species, including plants, animals, and marine life.

With a small rise in temperature, vegetation will be adversely affected at tropical latitudes: This statement is also correct. Tropical regions, which are already warm, might not cope well with even a small increase in temperature. Such changes can stress vegetation, especially species that are adapted to stable, narrow temperature ranges typical of tropical environments. This can lead to reduced productivity, changes in species composition, and increased vulnerability to pests and diseases.

A rapid rise in temperature may deplete shrub cover and only large trees will be able to survive:  In some ecosystems, a rapid rise in temperature could indeed stress or kill shrub species that are not adapted to higher temperatures, potentially leading to a dominance of larger trees that can better cope with these conditions. However, the opposite can also occur where trees are more adversely affected than shrubs due to factors like increased drought stress or pest outbreaks, leading to a landscape dominated by shrubs or grasses. 

Therefore, statements 1 and 2 are generally correct, while statement 3 is incorrect