A drought hits the habitat of a semi-aquatic bird population. All ponds dry up, and fish populations decline. There are two groups of birds in the population that differ in leg length and diet. Long-legged birds eat fish, while short-legged birds eat insects. The drought has little effect on insect populations. What is the main selective pressure in this scenario?
Answers
Kingdom Plantae, the plants:
-multicellular, photosynthetic organisms with rigid cell walls
-land plants evolved from aquatic green algae by evolving adaptations that allowed them to survive on land
-Land plants differ from water plants bc land plants need adaptations to help them find water and prevent its loss from the body
-They prevent water loss by a waterproof covering called the cuticle
-Cuticles prevent carbon dioxide diffusion, so they have openings called stomates
-Stomates also allow water loss, so plants can open and close them with guard cells to respond to changing conditions
-Most plants have evolved a system of tubes called a vascular system that allows them to transport materials around their bodies
-Plant vascular tissue has two parts
1) xylem moves water and minerals around the body
2) phloem moves food (sugar from photosynthesis)
-Air provides much less physical support than water
-Plants evolved a strengthening compound called lignin
-makes them strong enough to stand up in air
-found mainly in xylem cells
-Land plants' needs are met in two different environments: they need to grow in the air to get sunlight, but also in the soil to get water
-phloem is needed to move food to parts of the plant that can't photosynthesize
-Gametes cannot just be shed into the environment as algae do
-Gametes and young, small plants need to be protected from drying
-Cones, pollen and flowers are reproductive innovations evolved by higher groups of plants to assist in successful reproduction
4 major groups of plants
-based on their structures and type of reproduction
-Bryophytes are the most primitive type of plants
-Bryophytes are only partially cutinized and have no vascular tissue
-They remain small so water can diffuse around the body, and they live in moist environments
-Bryophytes don't have true leaves or roots, they have green photosynthetic leaf-like structures
-Some have root-like rhizoids under the body but they only help attach the plant, they are not specialized for water absorption
-Bryophytes produce sperm that swim from male to female plants, another reason that they must remain small
-After fertilization mosses also form spores and release them into the air to disperse new plants
-Seedless vascular plants evolved strong vascular tissue to transport food and water, allowing them to grow taller and bigger than mosses
-They have true leaves and roots
-The main evolutionary innovation of the seedless vascular plants was lignin, which allowed the evolution of xylem and phloem
-Mature ferns produce spores in sori on the undersides of leaves
-next evolutionary advance was the seed, first seen in the gymnosperms or cone-bearing trees, the pines, firs, redwoods, etc.
-Gymnosperms include the tallest and oldest plants known
-Gymnosperms' reproductive structures are very small and protected inside cones
-Female or seed cones produce the ovules
-Pollen is produced in separate pollen cones
-Gymnosperm sperm doesn't swim; it is moved in the air by floating pollen
-After pollen lands on the seed cone, it germinates and forms sperm
-These fertilize the eggs, which develop into seeds containing an embryo and some nutrition
-Most plants today are flowering plants or angiosperms; they have a unique reproductive organ, the flower
-Angiosperm also form seeds, which are protected inside fruits
-The greater speed of angiosperm reproduction allowed angiosperms to take over much of the area previously occupied by gymnosperms
-Angiosperms gave up fighting the height war and some evolved into smaller plants